A celebration of butterflies

I have gone through my files and made a selection of common butterflies to celebrate these beautiful insects in anticipation of the Big Butterfly Count, that starts tomorrow (16th to 31st of July) . This year it will last two weeks so there is more chances you can be out during good butterfly weather. You need to count what butterflies - and moths - you see in 15 minutes during a sunny spell. You can complete as many surveys as you want - from different days or different places - and you have time until the end of August to submit your records online. Click in the photo to start the slideshow.

Poisonous bug babies cluster together

These newborn green shieldbugs, Palomena prasina, look most unlike adults. They have a bright black-red warning colouration in their first instar, for a few days they cluster tightly together on top of their egg shells. After moulting into their second instar they change colour to green and black and they disperse away from their siblings. All shieldbugs, including nymphs have stink glands between the first and second pair of legs. If handled roughly they can release repellent chemicals and they are often brightly marked. But why do these bugs cluster together?
 The contrasting black and yellow or black and red patterns of Cinnabar moths, ladybirds, Burnet moths, bumblebees and wasps are visual signals to potential predators indicating that the animal is distasteful, poisonous or dangerous in some way. The predator, having had a nasty encounter with the aposematic organism learns to avoid it. But how does does aposematism evolve in the first place? You would think that the first aposematic individual either dies or is injured in the process, so it cannot be though natural selection, right? One possibility, first suggested by Sir Ronald Fisher in 1958 is aggregation of related aposematic organisms:

For, although with the adult insect the effect of increased distastefulness upon the actions of the predator will be merely to make that individual predator avoid all members of the persecuted species, and so, unless the individual attacked possibly survives, to confer no advantage upon its genotype, with gregarious larvae the effect will certainly be to give the increased protection especially to one particular group of larvae, probably brothers and sisters of the individual attacked. The selective potency of the avoidance of brothers will of course be only half as great as if the individual itself were protected; against this is to be set the fact that it applies to the whole of a possibly numerous brood

Fisher's hypothesis of kin selected aposematism has been questioned recently. Although aposematic organisms tend to be gregarious, phylogenetic analysis suggest that aposematism evolved before gregariousness, so aposematism makes gregariousness easier to evolve, and not the other way round.
 Birgitta Sillen-Tullberg carried out some elegant experiments showing that aposematism can give direct benefits to the individual, and that kin selection is unnecessary. She presented hand reared Great Tits (Parus major) with two colour forms of the same bug species (Lygaeus equestris), one grey and black (cryptic), and the other - the common form-  red and black (aposematic). A group of tits was presented with cryptic prey and another group with aposematic prey in 11 trials per bird. Great Tits learned to avoid both cryptic and aposematic prey - remember both are equally distasteful - but attacked cryptic prey more readily from the first trial.

In addition, when attacked, aposematic prey survived more, indicating that the tits were more wary when attacking it.
Being grouped, though, can confer further advantages. Gabriella Gamberale and Birgitta Tullberg carried out experiments testing the effect of grouped versus solitary prey - bugs, Spilostethus pandurus - on learning avoidance by predators - chicks in their experiments. Chicks learn to avoid aposematic shieldbugs in fewer predation attempts, and were less likely to attack twice they are aggregated than if the prey is solitary. They concluded that gregarious aposematic prey are a more effective signal for the chicks to learn, the reasons why this could be are still unclear.

References
Fisher, Ronald A. (1958). The Genetical Theory of Natural Selection Dover Publications, Inc. Other: 0-486-60466-7
Sillen-Tullberg, B. (1985). Higher survival of an aposematic than of a cryptic form of a distasteful bug. Oecologia, 67 (3), 411-415 DOI: 10.1007/BF00384948
Gamberale, Gabriella, & Tullberg, Birgitta S. (1996). Evidence for a more effective signal in aggregated aposematic prey. Animal Behaviour, 52 (3), 597-601 DOI: 10.1006/anbe.1996.0200

Face off

Ectemnius wasps are skilled fly hunters. Not only they hunt flies, but some species specialise in hoverflies, those masters of controlled flight. Like their prey, Ectemnius wasps are able to hover. As their large eyes suggest, they hunt visually and inspect flower patches that hoverflies frequent, hovering a bit, changing body direction, inspecting their terrain thoroughly. Once they detect a hoverfly, they try to approach from behind, and when at about 10 cm they aim and attack. Ectemnius provisions its nest - dug in dead wood - with hoverflies, which will serve as food for its larvae. The adults themselves feed on nectar. I was trying to photograph this digger wasp stalking hover flies, when it came across a male Syritta pipiens. The tiny hoverfly male, which often confronts other hoverfly males on this patch of wild rocket, instead of fleeing, it confronted the wasp, mirroring the predator movements and keeping his distance, both insects hovering perfectly still in front of each other for a few moments. Surprisingly, the wasp did not attack the fly and just moved on. Some insects have been shown to display a stealth strategy called "motion camouflage" by which an individual (the shadower) can conceal its movements to another individual (the shadowee) by maintaning its position in the retina of the shadowee. The shadower then appears as an stationary object from the point of vision of the shadowee. Some male hoverflies (and Syritta pipiens in particular) use this flying strategy to track females undetected and dragonflies use it to avoid being detected when intruding in other territories and it is also suspected to be used by visual insects when approaching prey. A range of models have been developed to simulate this strategy. Unsurprisingly, engineers are developing motion camouflage strategies to be applied to robots, satellites or with military purposes.
 According to Justh & Krishnaprasad:

Motion camouflage can be used by a predator to stealthily pursue the prey, but a motion-camouflage strategy can also be used by the prey to evade a predator. The only difference between the strategy of the predator and the strategy of the evader is that the predator seeks to approach the prey while maintaining motion camouflage, whereas the evader seeks to move away from the predator while maintaining motion camouflage.

I wonder if this was the case in the above photo. A temporary stale mate, but the prey got away.

References
Justh, E., & Krishnaprasad, P. (2006). Steering laws for motion camouflage Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 462 (2076), 3629-3643 DOI: 10.1098/rspa.2006.1742

Mizutani, A., Chahl, J., & Srinivasan, M. (2003). Insect behaviour: Motion camouflage in dragonflies. Nature, 423 (6940), 604-604 DOI: 10.1038/423604a

Fresh Holly blue shows its tongue

July is peak time for butterflies. What up to mid June seemed like a poor butterfly year is gearing up to a great one. Just today I watched 8 species locally. The most striking of them was this freshly emerged Holly Blue male. It is the first individual of the second generation I see this year. It basked in the morning sun in a front garden, and - unusually for this species - it sat with wings fully open for a while. Once warm, the butterfly closed its wings and fluttered onto another perch and stretched its tongue.

A more usual sitting posture for a Holly Blue, with closed wings

The butterfly with its short tongue stretched

Tongue length in butterflies is correlated with body length, so it is not surprising Lycaenids, the family to which the Holly Blue belongs, being small butterflies, have short tongues, around 8 mm. Whites and Brimstone and the Nymphalids have longer tongues, around 15 mm. For their length, some moths (such as the Hummingbird Hawkmoth) have very long tongues, 28 mm. The following table from Pollination and Floral Ecology by Pat Willmer illustrates the length differences between some butterflies and moths.

Tongue length determines the maximum depth of a flower corolla that a butterfly can take nectar from. Short tongued species prefer shallow flowers, often composite ones like brambles, tansy, hemp agrimony or dandelions.

Emerging harlequin ladybird

I collected 50 ladybird pupae (above) a couple of weeks ago. The idea was to wait and see what emerged from them to send records to the Ladybird Parasite Survey. After 6 days, 46 Harlequins had emerged, and from 2 of the remaining some tiny maggots of the parasitic phorid fly Phalacrotophora. Having so many ladybirds emerging at home meant I had a good chance to catch one of them emerging, something I had never seen before. I saw two, one of them almost right from the beginning, and this series of photos documents it. The whole process took about 10 minutes. In the next shot, the ladybird has broken the pupal skin and the pupal buds containing both pairs of wings are erect.

...she finally walks out. 

The ladybird then waits next to its pupal skin until she has hardened a bit and extends her wings, which are still yellow. You can see how the ladybird gets her spots in this post.