Corpse Camouflage and Termite fishing: Assassin bugs (part 2)

Right, well I hope you all enjoyed the previous post about the formidable Assassin Bugs of the Hemipteran family, Reduviidae, because I am back with more. In case you can’t tell, I love these insects and they’re not often talked about in mainstream media, so these posts aim to get the word out about these incredible predators. Following on from the previous post, this one will cover two more behaviours displayed by these Assassins.

*Apologies for the huge gap between posts, I was finishing the 4th year of my degree. Now that it is all done and I’ve had my results I’m planning on publishing posts much more frequently and consistently throughout summer.

Corpse Camouflage

We’ll kick things off with a behaviour that has both defensive and predatory uses, which I first learnt about by reading a paper with the brilliant name “Bugs with a Backpack” (Brandt and Mahsberg, 2002). It has been observed that the nymphs of the West African Assassin bugs from the Genera Paredocla and Acanthaspis cover themselves with, what is known as, a “dust coat” composed of dust (surprisingly), sand and soil particles (Brandt and Mahsberg, 2002). Furthermore, they pile up larger objects, such as empty prey cases, leaves and other foliage to form a backpack of debris (Weirauch, 2006). These particles and debris pieces are secured by secretions produced by specialised setae on their abdomens (Brandt and Mahsberg, 2002). This “backpack” appears to be mainly beneficial in defensive situations, particularly when they’re confronted by predators that rely on eyesight. It is thought that the backpack acts a disguise, making the bug look, well, less bug-like and therefore less likely to be investigated by a predator. Furthermore, the backpack can be shed (not unlike a lizard’s tail) should a predator grab onto it, enabling the bug to escape. The fascinating study by Brandt and Mahsberg (2002) did indeed show that those with a backpack had a higher survival when put in proximity to various predators (lizards, centipedes and spiders), than those with just the dust coat or nothing at all (see table 1.0). Spiders are not visually reliant predators and they did not  hesitate to attack the backpack wielding bugs, however, after biting into a pile of ants and detritus they tended to let go. And if they didn’t, then the backpack was ripped from the bug, giving it a chance to flee. The study tested a variety of hypotheses but I am risk of regurgitating the whole paper, so I’ll keep this short and leave a reference to the paper at the end.

One more interesting point that I will mention, is that it’s also considered possible that these bugs use the backpack to increase their hunting success. Acanthaspis concinnula lives in close proximity to nests of the fire ant species Solenopsis geminata and is a known predator of these ants. The backpacks of A. concinnula are often composed of previous meals of S. geminata. These fire ants are known to inspect their killed brethren and therefore will approach the assassin bugs with the corpses of their fellow ants on their back. This could act as a kind of bait for the assassin bug, resulting in less need for them to enter deep into the ant’s nest, but instead wait for the ants to come to them. This predatory use of the behaviour is likely to be widespread throughout the genera Acanthaspis as they are all known ant predators.

Furthermore, it is hypothesised that the dead ants could mask the scent of assassin bugs, enabling them to wander into the nest and around the ants undetected, again making predation easier. These predatory aspects of this behaviour have not been properly studied or conclusively determined, however it is a fascinating possibility. And brings me nicely onto the next, and final, assassin bug behaviour that I want to talk about.

Fishing for Termites

Salyavata variegata, a neotropical assassin bug found from Mexico to the southern region of the Amazon displays an interesting case of tool use to acquire its termite prey. But first, some background on the behaviour of its prey which enables them to be exploited in such a way. Nasutitermes corniger build ‘carton nests’ out of secretions produced by themselves and are often conical in shape and attached to tree trunks. The nests serve to keep out predators, prevent the termites from drying out and dying from desiccation, as well as to prevent flooding (McMahan, 1982). Therefore, it is crucial that the termites maintain its integrity and to this end, as soon a breach is discovered in the structure, workers immediately set to work fixing it. However, this predicable behaviour leaves them open to predation from the ever-ingenious assassin bugs. It was observed by McMahan (1982) who, whilst studying the termites had to open a small hole in their nest. Once the hole had been created, McMahan noticed something that resembled a piece of nest material move towards the entrance. However, that piece of nesting material turned out to be a well camouflaged Salyavata variegata assassin bug. Like those already mentioned, S. variegata had covered itself in dust and crumbled nest pieces, making itself incredibly well hidden. When the worker termites started to appear to fix the hole, the assassin bug reached over and snatched one up, to then quickly retreat and consume its catch. But the deviousness doesn’t stop there. Termites are also known to collect their fallen comrades and take them into the nest, often so that they can recycle the nutrients from the body. But again, this leaves them open to assassin bug trickery.

The S. variegata bugs were observed taking the empty shell of their previous termite meal and dangling it in the entrance of the hole, whilst maintaining a grip on it with their forelimbs. This attracted another worker who would grab onto the other end, only to find itself being pulled out through the hole. As soon as the second worker’s head was visible, the assassin bug would grip onto it and inject its deadly, toxic cocktail of digestive fluids and retreat with its new meal. This behaviour was seen repeatedly, even by a single individual. And once the hole had been closed up by the termites, the assassin bug didn’t stop. But instead would take the corpse of its most recent meal and push it into the still solidifying, soft, recently patched hole, effectively reopening it and enticing another worker out. Over a period of 3 hours, McMahan observed a single S. variegata nymph bait and feed on 31 successive termite workers, showing the voracious appetite of these bugs. Not only does the assassin bug dangle the dead termite, but it jiggles it around in a baiting-like manner, which when attempted by the researcher, only alarmed the termites, therefore, indicating that the bug has perfected the technique. Furthermore, by camouflaging itself in pieces from the nest, it potentially masks its scent, making the termites unable to detect it and further ensuring its hunting success. A truly ingenious and deadly technique displayed by these master assassins and a beautiful example of tool use.

Conclusion

Large charismatic predators often get all the attention, but after so many documentaries featuring them, I think it is time the ingenious, incredibly successful, predatory invertebrates deserve some attention. Starting with the deadly bugs of the Reduviidae family that have certainly earned the title of Assassin. The behaviours presented in these two posts are just a few of the tricks that assassin bugs have in their repertoire and we still have much to learn about them.

I hope you have enjoyed reading about these incredible insects, I have really enjoyed writing about them. I highly recommend reading the papers referenced below as they are brilliant studies and go into these behaviours in far more depth than I can in around 1000 words. The aim of these posts was to reveal the awesomeness of these insects to more people and hopefully encourage more reading and study on them. If you have enjoyed this post, feel free to leave a like, it is always hugely appreciated. And don’t forget to find me on twitter: Matthew Woodard @ZoologyNotes.

Thanks for reading, until next time.

Acknowledgements

Huge thanks to Orionmystery’s wildlife photography for giving me permission to use the awesome picture of the Acanthaspis petax nymph using the corpse camouflage. For more incredible wildlife photography check out their ‘Up close with Nature blog’ orionmystery.blogspot.com

 References

Brandt, M. and Mahsberg, D. (2002). Bugs with a backpack: the function of nymphal camouflage in the West African assassin bugs Paredocla and Acanthaspis spp. Animal Behaviour, 63(2), 277-84.

McMahan, E.A. (1982). Bait-and-capture strategy of a termite-eating assassin bug. Insectes Sociaux, 29(2), 346-51.

Weirauch, C. (2006). Anatomy of disguise: Camouflaging structures in nymphs of some Reduviidae (Heteroptera). American Museum Novitates, 3542, 1-18.