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Archive for November, 2010

Most predators rely on their camouflage and behaviour to get close enough to their prey to strike before the prey notices them and can take avoidance actions. A few predators, however, use an alternative plan – they don’t hide their presence but instead use deceptive means to stop the prey recognising that they are in fact a predator. These “aggressive mimics” use lures that represent a different species to trick their prey into coming closer; for example the anglerfish uses a dangling lure that imitates a worm or bug to encourage smaller fish to approach this ‘food’ before the small fish instead becomes the meal. Bolas spiders, by contrast, produce imitation female moth pheromones that lure male moths close enough to the spider to be caught.

An Australian research team has shown that assassin bugs of the species Stenolemus bituberus use two separate techniques to catch their spider prey. When stalking, the bug will slowly creep towards the spider until it is in striking distance. Its second technique is very different – the assassin bug will lure the spider to approach within striking distance by plucking the spider’s web threads, pretending to be prey caught in the spider’s web.

By comparing examples of web vibrations made by the assassin bugs to those made by actual struggling prey, falling leaves (which elicited no response from the spiders), and courting male spiders (which prompted the females to take up a mating position), the study demonstrated that the bugs specifically imitate the vibrations made by struggling prey. Spiders can be a dangerous prey that can counter-attack and eat the assassin bug instead, and high-frequency vibrations can lead to a fast, aggressive approach by the spider that could endanger the assassin bug. By mimicking weakly struggling prey using low-frequency vibrations instead, the assassin bug lures the spider into a slower, less dangerous (to the bug) approach by the spider that enables the bug to effectively draw the spider within attacking range for an easy arachnid meal.

Reference

Wignall AE and Taylor PW. 2010. Assassin bug uses aggressive mimicry to lure spider prey. Proceedings of the Royal Society B doi: 10.1098/rspb.2010.2060

Further Info

Angler fish
National Geographic
Sea and Sky
Arkive

Bolas spiders
University of Kentucky
Video of the spider lassoing prey (not for arachnophobes!)

Assassin bugs

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Researchers working in Papua New Guinea have analysed rainforest plant-herbivore interactions and found that an average of 251 herbivore (plant eating) species are associated with each rainforest tree species, 48 of which feed exclusively on that single tree species. With around 200 tree species in the lowland rainforest studied, this means the trees interact with somewhere in the region of 9,600 herbivorous insect species, which is staggering.

 Rainforest (thanks to tauntingpanda)Although these results used a fair amount of extrapolation of collected data from a limited research site and number of tree species, the research highlights the complexity of food-webs and inter-species relationships, particularly in ecosystems as species-rich as rainforests, and illustrates the huge number of species affected by the loss of each felled tree.

References

Novotny V et al 2010. Guild-specific patterns of species richness and host specialization in plant-herbivore food webs from a tropical forest. Journal of Animal Ecology 79: 1193-1203

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