Mating buff-tailed bumblebees

Next to a busy road, by the base of a tree, surrounded by concrete and oblivious to the noisy traffic, this pair of White-tailed bumblebees were mating this morning. The queen lying motionless, a bit sideways, the male tickling her rhythmically with his legs. I have been taking some videos with my camera lately to record some unusual, or more common bug behaviour. I hope this works as it is the first time I upload a video to BugBlog.

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I wrote the piece above almost 5 months ago, on the 19th of July, when I saw the bumblebees mating. I tried, and miserably failed to upload a video to YouTube. Here it is, finally posted. Thank you Crystal Ernst! More to come.

Birds and ant swarms

In July and August, typically in sunny days after rains, swarms of reproductive Black Garden Ants (Lasius niger) - winged queens and males - emerge from their nest to mate and start new colonies. Workers also come out en masse and run around the entrance of the nest, looking agitated. I had often noticed this and wondered why do workers did this, until yesterday, watching a Blackbird feeding on the winged ants coming out of their nests, realised why. The Blackbird run close to the entrance, fetched a winged ant and run away. The bird repeated this several times and was obviously being stung or sprayed by the ants around the nest, but still wanted to feed and its back-and-fro behaviour was evidence of the - at least partial - success of the frantic workers keeping predators at bay. Winged ant have many predators. Some casually feeding on the winged ones, others opportunistically making use of a plentiful, although ephemeral, bonanza. A range of birds fall in the latter category, starlings and sparrows feed on the winged ants - sometimes using fly-catcher techniques - and seagulls have been seen feeding on them up in the sky. While reading a paper on this, I remembered that last year, on the day the ants emerged, I looked up in the sky and saw many small flying things and thought they might be the flying ants. When I looked more closely I saw they were seagulls, and was surprised at how many there were, well over a hundred, soaring very high up. I took a shot (below) and forgot about it. They were most likely feeding on the winged ants that had been carried high by thermals in their swarming mating flight.

Seagull flock feeding on swarming ants (26/07/10)

This is the nest in the bottom right hand corner of the top photo

Workers around a nest with winged ants emerging (26/07/10)

Reference

James Baird and Andrew J. Meyerriecks (1965). Birds Feeding on an Ant Mating Swarm. The Wilson Bulletin, 77 (1), 89-91.
Gilbert S. Grant (1992) Opportunistic Foraging on Swarming Ants by Gulls, Shorebirds, and Grackles. The Chat, 56, 80-82.

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