Slug standing up

'Look, a slug standing up' called my 7 year old daughter. I went over by her and watched. Indeed, a Spanish Slug, Arion vulgaris, reared up as high as it could go in between some pots. It waved its body from side to side, and after some time it bent over itself turning round, touching its mucus pore with its head. I had seen this behaviour previously described in Rowson and colleagues' FSC guide 'Slugs of Britain and Ireland':

'Arionids are sometimes seen rearing up off the ground, as if sniffing the air' 

It is a curious behaviour of unclear function, are they really 'sniffing' the air? could they be sensing humidity in the air, assessing when to retreat to a refuge, or looking/smelling for food? Although slugs have very simple eyes, this rearing and moving side to side could allow them to assess where shadows are indicating plants to climb. Alternatively, they could be detecting or emitting pheromones to find or attract potential mates.

Fascinating jumping spiders

We had a very warm day today - for April - the sun hit the brick walls and this is something that brings jumping spiders out. I spot one on the wall, quite high up, she moves in a typical jerkily fashion on to a wooden plank and I take a few shots with my arms outstretched and a poor view of the LCD display, but I am happy when manage a few focused front shots (above). I think this is Salticus cingulatus, a close relative of the zebra jumping spider, Salticus scenicus. Jumping spiders, or salticidae - the family latin name - are the largest spider family, with 5,000 species. They have a highly acute visual sense, with their large and forward facing antero-median being responsible for the visual acuity, and the remaining 6 eyes - with the posterior pair facing almost backwards - acting as motion detectors. Although the external lenses are fixed, the internal eye tube can move to precisely look towards an object. Some species have been shown to have colour and UV vision (tetrachromatic vision) and correspondingly, jumping spiders include some of the most colourful spiders. Their mating rituals are mesmerising: they include synchronic front leg movements, abdomen vibrations and percussion, yes, percussion! They remind me of flamenco dancers with their tap shoes and castanets. Something that cannot be imagined and have to be seen:


I often come across feeding jumping spiders. Then they are preoccupied and they are much easier to approach. This male S. scenicus had caught a fly and came to inspect me, before returning to its oversized prey.

The following one, a tiny, possibly immature specimen still poorly marked, was preying on an aphid in my conservatory bougainvillea.

Jumping spider are extremely agile and their hunting has been compared to a cat stalking its prey. First the spider moves its "head" fixing its eyes on the potential prey, then the abdomen is aligned and then the spider moves slowly towards prey. When the prey is within jumping distance, the spider ties a line of silk to the substrate and pounces on the prey. Surprisingly, jumping spiders can detour when jumping, and approach does not need to be in a straight line, with the spider losing sight of prey in occasions, suggesting remarkable planning for a tiny invertebrate. Salticids show a range of predatory strategies from extreme sit-and-wait species which only move to jump into passing prey to specialist ant predators, to cleptoparasitic species, which specialise in robbing spider webs or deceptive prey-mimics, who imitate the movement of prey that has fallen on a web to lure the spider out and the eating the spiders themselves. There is even a herbivorous jumping spider, the just so named Bagheera kiplingii, from Mexico, which exploits an ant-acacia mutualism, mainly  feeding on specialised leaf tips produced by the acacia for its mutualistic ant, and nectar, complementing its diet with a few ant larvae. What amazing animals they are.

References
Richman, David B., & Jackson, Robert R. (1992). A review of the ethology of jumping spiders Bulletin of the British Arachnological Society, 9 (2), 33-37

Meehan CJ, Olson EJ, Reudink MW, Kyser TK, & Curry RL (2009). Herbivory in a spider through exploitation of an ant-plant mutualism. Current biology : CB, 19 (19) PMID: 19825348

Red Mason bee male tactics

I posted about the Red Mason Bees (Osmia rufa) nesting in our bee post last year. The males  have now been active for a few weeks, and they are quite interesting to watch, as they are very inquisitive and interactive with other insects. The different behaviours of male bees depend to some extent on how the resources used by females - such as nesting sites and food plants - are distributed. These resources indicate where females are to be found, and to maximise their reproduction males are to encounter and mate with as many recently emerged females as possible. In Osmia rufa, females are thought to mate only once shortly after emerging from their nest, as males guard females after mating and impregnate them with chemicals that make the females unattractive to other males, effectively ensuring their paternity. As many other bee species, Red Mason Bees are polylectic - they are quite generalistic as to what flower species they feed on - and their nests are quite scattered (at least in natural habitats!), and therefore it does not pay to be territorial. In a 1988 paper I read today, Karsten Seidelmann graphically described Red Mason Bee behaviour based on 364 individually marked males:

In order to find mates, each male roamed about his home range. These home ranges were located around flowering groups of foods plants, but also by nesting places. Occasionally sunny places (exposed leaves, stones, etc.) or bushes of dwarf pine in the surrounding of large nest aggregations were inspected and patrolled as well. Home ranges sometimes also consisted of several small patchy encounter sites. Males then searched within the patches and flew in a straight line between them. Every home range contained an exposed sunny place where the resident male basked between patrol flights at irregular intervals. When home ranges become shadowed, males turned to other areas, returning when the area was in the sun again. Areas abandoned because of shadows were not occupied by other males.


The photo heading this post shows a male next to a potential nesting hole in our bee post. The males often enter and inspect the holes and look out.
These little bees often chase and make contact with other bees - not only of their own species but also other insects such as butterflies in their home range - and I had misinterpreted this behaviour as agressive, an indication of territorial behaviour. Seidelman's detailed observations, on the contrary, shows that the Red Mason Bee is not territorial. It does have a 'home range' but these are not exclusive to one individual and home ranges of different males partially or totally overlap. Males also occasionally went on 'excursions' away of their home range. Their chasing and making contact with other visually detected insects is an 'inspection' behaviour: they check if they are conspecific females or not, but they do not attempt to drive them away:

Home ranges ranged from 3 to 30 m2 in size. Males continuously altered their home ranges in response to changes in possible encounter sites. Plants that started to flower were integrated in adjacent home ranges, or new home ranges were established and old ones were abandoned. If females emerged from a large aggregation of nests, the searching activities of several males were concentrated entirely on these nesting places, with males inspecting nest entrances frequently.
Males inspected all resting and flying insects with an O. rufa-like shape during their patrol flights. They approached other solitary bees (e.g., Osmia, Megachile, Anthophora, Andrena), as well as honeybees (Apis), bumblebees (Bombus), or even flies (e.g., Calliphora). However, only receptive females of their own species were mounted, whereas males of O. rufa and other insects were abandoned immediately after a short contact.


Seidelman also analysed the reproductive success of males, that is, how many times they mated throughout their lives and concluded that this is independent of the male body size.

More information at:
Karsten Seidelmann (1999) The Race for Females: The Mating System of the Red Mason Bee, Osmia rufa (L.) (Hymenoptera: Megachilidae). Journal of Insect Behavior, Vol. 12:13-25. here.

Robert John Paxton (2005) Male mating behaviour and mating systems of bees: an overview. Apidologie 36:145–156. here.