Larvae in a poo costume

Of all insect larvae I have come across, these have been the trickiest to spot. Red Lily Beetle adults were mating and laying eggs on my Asiatic lilies this afternoon. I was sitting next to the lilies and I was intent on spotting the larvae. It took a while. They look exactly like wet caterpillar poo. 

The bright orange eggs are laid in rows under the leaf, and when the larvae hatch they stay together and start eating the leaf where they have been born, their slimy droppings are deposited on their back, forming a faecal shield which grows in size with the larvae. The faecal shield disguises the larva, presumably helping to protect them from predators. When small, larvae fed on the underside of the leaf, leaving the upper leaf surface withered. As they grow they disperse from their siblings and they may move to the upper side of the leaf, eating the whole leaf or flowers as they grow. If they feel disturbed, they completely retreat inside their fecal shield, when they relax, their shiny black head and short legs are visible (above). The fully developed larvae drop to the soil where they make a white cocoon. There is a single generation a year, the new generation of beetles emerges and feeds before overwintering in the soil.

A string of lily beetle eggs

A cluster of young larvae - the leaf has been turned upside down to take the photo. The withered end of the leaf can be seen in the background

Tree sculptures and lesser stag beetles

In the last three weeks, I have been coming across Lesser Stag Beetles (Dorcus parallelipipedus) dead on the pavements in my street. June and July are peak emergence time for these dark, flattened beetles. Today we found 10 squished ones and a live one next to a chestnut tree stump, is this were they were coming from? I got the impression that the beetles might have been seeking shelter under the wheels of a car parked next to the stump, and they were inadvertently squashed every time the car moved. This tree stump used to be a tree sculpture (here for a photo, yes, the car behind is the beetle squasher!). Old trees that have got too big are partially felled in our neighborhood to avoid subsidence and then carved into statues. The dry dead wood soon becomes peppered with many tiny beetle holes, which are taken over by little wasps to nest, accompanied by their suit of parasitoids. The sculpture was taken down last year as it had started to rot and become unstable. The remaining stump was as soft as crumble. When I looked into it today, many large exit holes were visible on the surface. I dug a bit into the rotting wood with a stick and it didn't take long to find a Lesser Stag Beetle larvae. They have a large head, strong dark mandibles to chew the rotting wood and a c-shaped body curled underneath. The larva was very active, it turned round and quickly moved away hiding into the wood. Millipedes, woodlice and earthworms shared the dead wood with the beetle larva.

The collection of dead Lesser stag Beetles. The one on the bottom left-hand side is a large male with impressive jaws. There is huge variation in size amongst individuals.

A close up of the stump with exit holes.

An overview of the Chestnut tree stump

A side view of the young larva

Lesser Stag Beetle larvae take over two years to develop, and several stages may coexist in the same stump. Adults also may live several years, so it is a shame so many are dead, but this stump probably holds many tens of larvae and many adults have probably already dispersed successfully after emergence. 

Neriene montana egg guarding

The contrasting red background of a kids wheelbarrow, made it easy to spot the egg sac of this Neriene montana female. The yellow eggs are visible through the loose, gauze-like silk wrapping of the egg sac. The female hangs upside down on her hammock web by the egg sac. She may possibly be able to lay more egg batches, as the female lives up to 7 months. Although egg guarding has not been reported in many money spiders and I could find very little on the reproductive behavior of this species, this photo confirms that the eggs may be laid very close to the web and will undoubtedly benefit from the female being nearby.

Six or eight legged bug army fighting aphids

 Neat rows of black aphids suck the sap of one of the stems of a Lesser Knapweed in the garden. This morning, I notice a hoverfly, Syrphus ribesii, around, she lands near them, flies straight to the top of the aphid group and curves her swollen, pointy abdomen towards the branch. She is egg laying, notice two elongated white eggs near her in the top shot. She came back again to lay more eggs near the same spot. Hoverfly larvae feeds voraciously on aphids and female hoverflies choose the best spots to maximise the chances of their offpring thriving. Aphids populations are booming now and several groups of insects and spiders exploit them as their predators and parasites, as illustrated in the following shots.

A hoverfly larvae eating an aphid in the roses.

A parasitic wasp approaches a group of elder aphids. She will inject an egg into the body of an aphid and the wasp larvae will develop inside it.

This other wasp is laying eggs inside the aphids.

Adult 7 spot ladybird eating an aphid on rose.

Araneus diadematus spiderling on its web with a captured winged aphid

Late instar harlequin larvae with aphid

Philodromus spider with prey

And a jumping spider

A mirid flower bug nymph, Anthocoris sp. sucking the juices of the aphid in much the same way the aphid does it to plants.

Girl power: sex and parthenogenesis in Vine Weevils

Precariously perched on a young oak branch, a Black Vine weevil, Otiorhynchus sulcatus, the first of the year. I am really not looking forward to seeing them, but they have an intriguing life cycle, which is key to their success. The Black Vine weevil is a generalist feeder which in the early 19th century was only known in a small area in Central Europe and since then has expanded to much of the world aided by human activities and has become a pest of a range of agricultural and horticultural plants, despite being a flightless, sluggish insect.
 The remarkable thing about them is that all Black Vine Weevils are female. A weevil does not need to find a partner to mate before reproducing, she just emerges from the soil, stumbles to the next suitable patch and lay eggs. The next generation of daughters will be genetically identical to their mum, forming natural clones. Parthenogenetic lineages in general are good colonisers, and expand their population ranges more easily than their sexual relatives. Individuals might disperse the same distance during their lives, but in the parthenogenetic species a single individual can successfully colonise a new patch and establish a new population, while the sexual species needs at least two individuals of different sex - or a fertilised female - and then has to cope with the disadvantages of inbreeding if it succeeds. Most parthenogenetic insect species are flightless, which suggests that parthenogenesis is more advantageous if the insect is naturally a poor disperser.
But there is another card up the weevil sleeve. These beetles are triploids, instead of having the usual two sets of chromosomes (that is, being diploids, like us) they have three. Polyploids are often larger than diploids and may enjoy further ecological benefits such as more resistance to the cold or wider ecological tolerances. Ecologically, parthenogenetic weevils have moved much from their origins in the moist valleys of the Alps, and are now able to persist even indoors, munching the roots of plant pots.
They might not be the most attractive insects, but these weevil story of success shows that appearances can be deceiving and that, sometimes, girls rule.

More information

Lundmark M (2010). Otiorhynchus sulcatus, an autopolyploid general-purpose genotype species? Hereditas, 147 (6), 278-82 PMID: 21166797