Bees in ponds

When you think about a pond, bees do not normally spring to mind. Bees, however, need water. In sunny days honeybees travel in numbers to water sources to take water to cool down their hive, and they also use it to dilute honey to feed their larvae. These three were drinking by the edge of the pond in my local wildlife garden, near their hive.

On the other side of the pond edge there is a muddy site. Several female Red Mason Bees (above) were collecting mud to line and cap their cells. A female would dig up the mud and shape it with the  help of her jaws and two little facial horns into a little ball, and then fly to the nest holding the ball in her jaws. It took me a few attempts to get a half decent shot.

Osmia rufa female with her ball of mud

Racing male tree bumblebees

In the last two weeks, the garden has been overtaken by frenzied male bumblebees. They follow a set circuit, round and round, racing from bush to bush and then having a little bumble in each. If you wait for a bit on a particular spot on the route, you are likely to see another bumblebee a few minutes later passing by in the same direction, doing exactly the same. Most of the males I have been able to identify doing this are Bombus hypnorum. Today, a male B. hypnorum - which can be distinguished from the female by his white moustache - got trapped inside the conservatory and I had his portrait taken (above). Many male bumblebees have recently emerged from their nests, never to return, and their mission is to find queens and mate with as many as possible. In many bumblebee species, males' strategy consists on tracing a route, sometimes hundreds of meters long, often circular, depending on the species, and marking certain places along the route with pheromones produced by scent glands in their jaws. Males join already set routes and therefore many males, some of them probably their siblings, go round the same routes every day, stopping to feed occasionally. Queens encountering a route are attracted by the pheromone and are then intercepted by males. The discovery and first description of these male bumblebee flight paths - from Bombus hortorum males - dates back to Charles Darwin, from observations he carried out at Down House. Although he didn't realise pheromones were involved, he noticed bumblebee routes and them stopping and bumbling at places he called "buzzing places", and marveled at the fact that the same or very similar routes were used year after year:

I then followed their route for about a hundred and fifty yards until they came to a tall ash, and all along this line they buzzed at various fixed spots. At the far end, near a pollard oak, the track divided into two as shown in the plan. On some days all the bees flew in the direction I have described, but on others some arrived from the opposite direction. From observations made on favourable days, I think that the majority of individuals must fly in a wide circle. They stop every now and then to suck at flowers. I confirmed that whilst in flight they move at about ten miles an hour, but they lose a considerable amount of time at the buzzing places. The routes remain the same for a considerable time, and the buzzing places are fixed within an inch. I was able to prove this by stationing five or six of my children each close to a buzzing place, and telling the one farthest away to shout out " here is a bee " as soon as one was buzzing around. The others followed this up, so that the same cry of " here is a bee " was passed on from child to child without interruption until the bees reached the buzzing place where I myself was standing.

  This sketch of the grounds of Down House shows the part of the male bumblebee flight route studied by Darwin with the help of his children. What fun must have been to have him as a dad!

References

Freeman, R.B. (1968). Charles Darwin on the routes of male bumblebees. BULLETIN OF THE BRITISH MUSEUM (NATURAL HISTORY) HISTORICAL SERIES , 3 (6), 177-189.


Stiles, Edmund W. (1976). Comparison of Male Bumblebee Flight Paths: temperate and tropical. Journal of the Kansas Entomological Society., 49 (2), 266-274.

Tree bumblebee with foxglove

It is the 10th anniversary of the first recorded British Tree Bumblebee, a continental European species which crossed the channel on 2001, esblished successfully and has spread since to much of England. It's natural colonisation has been closely followed by Stuart Roberts, from the Bees, Wasps & Ants Recording Society (BWARS), who is collating a survey of this spread and has published an information sheet. The bumblebee is very easy to identify, with a tawny thorax and a black abdomen and a white tail. If you have any records you'd like to submit, check the website for more information. In my area, the tree bumblebee is doing really well and it is one of the commonest species at the moment. You can see them foraging on Ceanothus, cotoneaster, brambles and snowberry flowers. Today is the first time I have encountered them feeding on Foxgloves. This individual visited several spikes in succession, given me the chance to get a shot.

A blue glass snail

When lifting a pot to plant out today, I found this Glass Snail. There are four British species, and I think this is Oxychilus draparnaudi, given its relatively large size (a mighty 15 mm). Glass snails are named after their shiny, fragile and translucent shells when alive. After weathering the shells rapidly lose their lustre. Oxychilus shells are rather flat, which makes it easier for them to hide under pots or stones.

Given their small size - and their association with pots, nurseries and greenhouses - it is not surprising that several European Glass Snail species have been inadvertently introduced in temperate or subtropical regions around the world, including New Zealand, Australia and the U.S. and Canada. What perhaps is unexpected is that many Glass Snails, including O. draparnaudi are predators and their diet include other snails and slugs and their eggs, in addition to worms, and dead insects. They have even been reported to eat Garden Snails. When predating on snails, they attack the snail's body first with their radula and when they cannot access more flesh from the outside, they drill a hole on the shell to finish off their meal. The introduced populations, however, can be a threat for the native snail fauna and reductions or losses of local snail populations have been reported in areas with these predatory snails when compared with patches where they were absent in the U.S and New Zealand.

References
Barker, G.M. (2004). Natural enemies of terrestrial molluscs. CABI. DOI: 10.1079/9780851993195.0279. Here.
Karin Mahlfeld, Karin. Impact of introduced gastropods on molluscan communities, northern North Island. here.

A handsome snail

After a light shower yesterday, garden snails came out of their shells and went on a walkabout in search for food. Snails get some bad press in gardening circles, but most of my garden snails are feeding on the ground, on dandelion leaves or fallen vegetal material - OK, I am an untidy gardener now you know. I found this beautiful individual and thought I would take its portrait. It behaved quite well on a white plate and here you have it, on its best side.

Robbing and Buzzing

I took this shot of a male Bombus pratorum nectar robbing a few days ago: the bee's short tongue is inserted into a hole previously pierced at the base of the flower, where it can easily reach the nectaries. The other flower on the right has also these "drinking holes", which once present, are used by short or long tongued bees alike. The first B. pratorum workers of the year, which are very small, do appear to be able to feed through the corolla opening, and often visit intact comfrey flowers. A possibility is that the small workers are actually just collecting pollen - not nectar - using a  "buzzing" technique. This consists on holding onto the flower and then vibrating its wings - and making a characteristic high pitch sound. At certain vibratory frequencies, the pollen becomes dislodged from anthers and streams out of the flower, where is gathered by the bee.

B. pratorum worker collecting comfrey pollen, note the white pollen baskets

You might have seen bumblebees buzzing on poppies, as that way they dislogde much pollen, which covers their hairy bodies and that they then collect into their pollen baskets. These buzzing visits by bumblebees are common in several species, including comfrey, borage and kiwifruit and some of these flowers are actually pollinated this way. Not only B. pratorum, but other bumblebee species gather pollen in this way. Despite being relatively common, this behaviour is easily overlooked, for example, if you spot the bees casually, or from some distance, or there is background noise, but you can see the difference in sound between a bee collecting nectar (the first bee in the video, a B. pascuorum) and bee collecting pollen (a B. pratorum) in Comfrey in this YouTube video by pixiebaggins:

A resourceful bumblebee

Iris flowers are tricky for bees. They are quite unlike other flowers. Basically, each flower is made of a wide landing platform with striking nectar guides, but to be able to collect the nectar, bees have to push through a lip pressing against this platform - on top of this lip are first the stigma and then the anthers. As the bee enters, it often looks like it has to press with some force to lift the lip to form a gullet high enough. As she enters, its back presses against the stigma, depositing any pollen it might carry; then her back rubs against the flower's anthers, collecting some pollen. On her way back, the bee presses the stigma against a groove, so preventing self-fertilisation. This contraption ensures that visited flowers get cross-pollinated. Long-tongued bumblebees, Bombus hortorum and B. pascuorum and fork-tailed flower bees, Anthophora furcata, are able to enter the flower and feed the way the flower intended. Today I saw a buff-tailed bumblebee, Bombus terrestris, landing on the flowers of Iris versicolor, and appearing to have sensed there was nectar in them, tried in various ways to enter a flower, failing. The bumblebee started then biting the flower lip, in an unsuccessful attempt to gain entrance (top, check its jaws wide open). In other posts I have dealt with this piercing technique used to successfully steal nectar from tubular flowers like comfrey and honeysuckle, where this short-tongued bumblebee cannot reach the nectar.

Not this way - it missed the entrance and got on top of the lid

not this way either...

... and probing with its tongue for nectar after biting the flower lip.

Although this bumblebee was unsuccessful this time, the persistence of its behaviour after failing to get nectar first time round attests to the resourceful behaviour of this successful bumblebee.

Two summer bees

The Summer season is quickly advancing this year. This week, Stachys sylvatica, the hedge woundwort, came into blossom and it has quickly being followed by the first Anthophora furcata males, which I saw yesterday visiting the sage, the foxgloves and Lamium maculatum. The previous two years I spotted the first males on the 7th and 10th of June, so the 21st of May is very early indeed.

Anthophora furcata male visiting sage

 The second summer bee is the leaf-cutter bee, Megachile. I think I have already seen the two species that visit my garden this year. The first one, a female Megachile centuncularis (tentative ID) cold on a Cat's Ears, Hypochoeris radicata, on the 16th of May.

Megachile centuncularis on Cat's Ears

The second, a just emerged male M. willughbiella, peeking out from its cell in the bee hotel, its white-golden gloves visible (top photo) on the 18th (top photo). A few moments later, a male was sunnying itself, stretching its abdomen, and grooming itself on a branch nearby and flying away into the wide world.

A fresh Megachile willughbiella male stretching its jaws and showing its white gloves

This small bee hotel -placed in a sheltered, sunny fence in the garden - has been very popular with bees this season, and many of last year's cells have produced bees. You can see the muddy remaining of the walls of last years nests around some of the openings in the photo above -, and several others have been completed this year by red mason bees, Osmia rufa, which are still active.

A bug eating plant in the garden

Ever since I've had teasels (Dipsacus fullonum) in the garden, I have wondered why each joined-up pair of leaves catches and holds rainwater like cups. This fact has been remarked by numerous botanists for a long time. As early as 1875, Francis Darwin, son of Charles, observed how these rain-filled cups trapped many invertebrates, including slugs, who drowned and whose bodies decomposed in the water, and described the plants adaptation to catch the insects:

it is quite certain that the plant is well adapted for catching and drowning insects.
The connate leaves form cups holding from 12 to 100 c.c. of fluid ; the leaves are smooth (although those of the seedlings are rough, with large prickly hairs) and are inclined so as to form a large angle with the horizon and a small one with the vertical; they form, therefore, two steep and slippery slides, leading to a pool of water. The stalk of the plant is covered with sharp prickles, but these cease where the stalk dips into the water in the cup. If it were not for the loss of the prickles at this point, a ladder of escape would be provided for the drowning victims. I have seen a beetle struggling to get out, and observed his tarsi slipping over and over again on the smooth stalk. The cups undoubtedly form a most efficient trap. In
some wild teasels the following insects were found:—In one cup six large malacoderm beetles, from half to three quarters of an inch in length, one fair-sized caterpillar, and two flies; in another, seven of the same beetles, one earwig, a bluebottle fly, besides many smaller flies and much debris.

Francis Darwin cited his great-grandfather Erasmus, who, the previous century, hypothesized that the teasel cups actually protected the nectar from insects, being unaware of the relationships between flowers and insects. Frances, who thought the teasel was a carnivorous plant, went on to investigate how teasels could absorb the nutrients afforded by the insects and made numerous, if somewhat puzzling, experiments on some glandular cells and filaments produced by the leaves. He also explained how beetles died faster in teasel water than in pure water, as if the teasel produced some chemical to "narcotize" them. Francis Darwin believed that the teasel benefited from these catched insects, and even designed the experiment to prove it:

I hope to decide by a comparative experiment, in which a number of teasels raised from seed under similar conditions will be divided into two lots, one half being starved and the other fed with insects or pieces of meat.

Unfortunately, apparently, he never carried out or published this experiment and therefore, could not provide the key test to show that the teasel was a carnivorous plant. These key experiments had to wait over a century. A few weeks ago Peter Shaw and Kyle Shackleton published a paper finally showing that the teasel is actually a carnivorous plant. They carried out field experiments treating teasels in one of three ways: (1) removing all insects in the cups one a week; (2) supplementing the cups with a dead maggot larvae a week (fed treatment) or leaving the teasels as they were (control). Their results show that although the treatments had no effect of the size attained by the plant, supplementing the plants did increase the weight of seeds set by 30%.

I thought I'd post on this topic once I came across some teasels and could get some drowned insect shots. This week I kept an eye on a teasel growing in a neighbours' garden and this is the result. A spider (above) and a dipteran (below) falling prey to this intriguing plant. The shots are from the same set of leaves.

References

Shaw PJ, & Shackleton K (2011). Carnivory in the teasel Dipsacus fullonum--the effect of experimental feeding on growth and seed set. PloS one, 6 (3) PMID: 21445274
Darwin, F. (1877). On the Protrusion of Protoplasmic Filaments from the Glandular Hairs of the Common Teasel (Dipsacus sylvestris). Proceedings of the Royal Society of London, 26 (179-184), 4-8 DOI: 10.1098/rspl.1877.0003

Tiny snails on cockle shells

My daughter found some tiny snails under a cockle shell in a pot yesterday. I took some photos but I could not identify them so today I went to find them again and try and take some shots of the more informative mouth of the shell. There were five or six of them, that were now active after last night's rain.

I looked in the pot and I found dozens of them. I had never seen them before and we had a whole pot population of these 2 mm or so snails happily living in the garden! Fauna, from WAB, identified my photos of the shell mouth today as Lauria cylindracea, a very common and widespread snail in the U.K. A favourite habitat is on stone walls covered on Ivy, but also lives in moss, leaf litter and crevices of old trees, habitats not particularly wet. It feeds on fungus growing on the dead leaves.
 As many snails, individuals of L. cyclindracea are hermaphrodites, which mate with each other to fertilize their eggs. This species, however, is relatively unusual for a snail in that it is ovoviviparous. It retains its eggs - 4 to 6 -inside its body until they hatch, and they are born into miniature snails, even tinier than their parents. Some of these juveniles were also present under the shell near the adults. The snails reach maturity at two years old and can live over 5 years, reaching a maximum size of a mighty 3.5 mm.

 In their study of life history and reproduction of L. cylindracea in Israel, Heller and collaborators discussed what evolutionary forces might have led to the evolution of ovoviviparity in this species. They hypothesize that a combination of small size - which limits the total number and the size of the eggs that can be produced - and high egg mortality, for example due to drought or lack of appropriate egg laying sites or inability to bury the eggs, are the key selective pressures. That way, offspring are born right next to their parents at the conditions most suitable for survival. The snails can also determine up to some point when the birth happen, retaining the juveniles longer when the conditions are very dry, and quickly giving birth when favourable moisture conditions return, that way maximising the chances of their offsprings survival. Heller and collaborators state:

Active hatchlings are advantageous, as compared to eggs, in that they can immediately start to feed, grow, fight off fungi, cope with brief periods of desiccation by moving into deeper layers of litter or temporarily retreating into their shell, and avoid drowning (or being washed away) as a result of occasional flooding of the riparian litter habitat, by moving into higher layers.

They compared this reproductive strategy in minute snails with the situation in larger species:

Large snails can produce eggs in vast numbers. Further, lack of size constraints enables the large adult to lay large eggs, generously coated with thick layers of albumin and mucus to tide the developing embryos over varying periods of drought and hunger. In Helix texfa, a species of 40 mm and 4.3 g (found in Israel very close to our present study site), each single egg averages 5.5 mm in size and 70 mg in wet weight (bigger and heavier than an entire adult Lauria), an adult produces 60 eggs per clutch, and clutch weight represents about 10% of body weight (Heller & Ittiel, 1990). In large snails with large clutches also sib cannibalism may occur, thereby increasing survival chances of the first individual to hatch (Baur, 1994). Further, large oviparous snails frequently deposit their eggs into pockets in moist soil. A deep cavity lined with mucus can protect the eggs against bacteria and fungi (Baur, 1994); it also enables the deposition of eggs in soil layers that remain damp for longer periods of time, and thereby reduces risks of desiccation. The cavity is dug out by the snail’s foot, so its depth is broadly correlated to foot size. Helix can dig 5cm into moist soil and Arclzachatina can dig a 15 cm cavity in one night (Tompa, 1984; Baur, 1994). Minute snails, however, do not have the potential to dig much beyond 0.2cm (except for subterranean genera, see Heller, Pimstein & Vaginsky, 1991). They can either dig minute cavities, or deposit their eggs in damp litter, where they would be exposed to fungi. Ovoviviparity may thus be a mode of parental care for snails that can neither lay many eggs, nor big eggs, nor dig deep egg cavities.

I will keep looking for these snails to see how widespread they are in the garden. I wouldn't be surprised to have overlooked these fascinating creatures due to their minute size. Were not for the white background of the shell where we found them we would have probably missed them altogether.

Reference
Heller, J., Sivan, N. & Hodgson, A. (1997). Reproductive biology and population dynamics of an ovoviviparous land snail (Pupillidae). Journal of Zoology, 243 (2), 263-280 DOI: 10.1111/j.1469-7998.1997.tb02781.x

Tree bees. 1. Holly.

These days I am looking up trying to find bees in trees. Insect pollinated trees can attract large numbers of bees, as they offer a highly concentrated resource: hundreds or thousands of flowers are present in the same spot. The drawback for the bee watcher is that, unless you carry binoculars, identification is not easy. There are two holly trees in my garden and I had noticed patrolling Red mining bees and feeding Bombus hypnorum in them before, but I could not take good shots. Today I found a holly hedge in bloom and I could get close to the bees that pollinate this tree. Holly flowers are small and inconspicuous and I have rarely noticed bees visiting them, but this little bush had many bees in it. Hollies are dioecious, which means that there are male and female trees, self-pollination is not possible and fertilisation requires insects visiting first a male tree and then a female tree. I am not sure if male holly flowers produce nectar as well as pollen. On the photo above a male Red Mining bee sits on the flowers of a male holly, its antennae covered on pollen.
In their Holly monograph, G. F. Peterken and P. S. Lloyd stated:

Entomophilous. Apis mellifera L. is the commonest insect visitor, but the following bees have been observed in southern England (O. W. Richards): Andrena wilkella Kby. (Andrenidae), Osmia rufa L. (Megachilidae) and Bombus lucorum L. (Apidae). B. lucorum and syrphid flies have been seen at the flowers in northern England. Nectar is secreted from tissue at the base of the ovary.

A honeybee visiting the flowers.

An Red Mining bee at the left of the flowers with scopa full of yellow holly pollen

Reference:

Peterken, G., & Lloyd, P. (1967). Ilex Aquifolium L. The Journal of Ecology, 55 (3) DOI: 10.2307/2258429

Vine weevils!

I do not like all bugs. I like my pot plants and that's why one of the villains in the garden is the Black Vine Weevil, Otiorhynchus sulcatus (adult above). The larvae of this weevil feed on the roots of many types of plants. In pots, especially indoors, where there are fewer parasites and predators and root growth is restricted they thrive and cause havoc. They overwinter in the soil as larvae and start feeding underground as temperatures increase. By the time they pupate most plants host to this species will be dead. If they are succulents, their root system is gone and the stems fall out of the pot one by one. I have a pot of strawberries from last year. At the end of the winter they had a few little offshoots which I planned to pot out. But they all died and shrivelled and there was only some ghost strawberry plants clinging to life left. I took the plants out today and came across the culprits: several larvae and dozens of pupae of Vine Weevil.

Three pupae and a fully developed larva of Black Vine Weevil

The adults emerge from the soil around June, they climb clumsily out and wander in search of food. They feed on leaves at night, leaving tell-tale C marks on the edge of leaves. They appear slow and harmless, and are unable to fly, but they can climb very well and feign being dead and drop to the ground if disturbed, so they tend to be left alone. Adults are all females which reproduce by parthenogenesis giving origin to genetically identical daughters. They can start reproducing by themselves as soon as they are ready, no need to waste time looking for a male and mating, and when they are, they go for it in earnest. At 21 oC, their optimal temperature, they can lay over 1000 eggs over their lifetime of four or five months. This mode of reproduction coupled with its preferred niche in the ornamental and agricultural trade has allowed this species to thrive and expand across the world from their native Europe, so, although I do not like it, I do marvel at its successful life history. What next? We should be getting some parasitic nematodes and watering the pots with them in the hope that they will infect the pupae and stop the invasion.