Is the distant relative of the stink bug an excellent hunter?

Midsummer is here, and it's the time of year when insects are at their peak. Some of them are already familiar to us, but there are others that you may not be familiar with. There is a type of insect that you may encounter from time to time, but you often overlook it because it looks unremarkable. In fact, they are very famous in the "insect world"! They are assassin bugs.

01Ugly , but sharp

Figure 1: The mouthparts of the assassin bug are very sharp (copyright image of the library, reprinting may cause copyright disputes)

Assassin bugs are not good-looking, with small heads and bulging eyes, and their bodies give people a sense of smell: they are distant relatives of "stinky bugs" and belong to the stink bug family. Stink bugs belong to the order Hemiptera in the class Insecta in biological taxonomy. "Stinky bugs" usually refer to some insects in the family Pentatomidae, such as the brown-winged stink bug ( Halyomorpha halys ); while most stink bugs that can be called assassin bugs belong to the family Reduviidae, which is a large insect group with about 7,000 known species. Although the bodies of assassin bugs look narrower, they still look very similar to each other, and at least it is known that many assassin bugs can indeed release a stench through their scent glands when threatened, and the stench released by some assassin bugs is very strong.

However, releasing odor is only a traditional skill of assassin bugs. What's more sharp is that most assassin bugs are ferocious predatory insects. The front legs of assassin bugs can hold prey like a mantis, but their front legs do not need to be as strong as a mantis, because the piercing and sucking mouthparts of assassin bugs are much more dangerous than the chewing mouthparts of a mantis. It is like a thick cone that can easily break the body wall of the prey and then forcefully inject venom into it. Their venom is very powerful and can almost instantly make the prey lose the ability to resist.

Like most insects, most assassin bugs have little interest in humans. Their targets are other insects. But the cone assassin bug is an exception. The English common name of the cone assassin bug is "kissing bug", which literally means "kissing bug". There are about 150 species of cone assassin bugs. They feed on the blood of vertebrates and can spread diseases. Some of them will actively seek out humans and can spread American trypanosomiasis. Fortunately, the probability of encountering such a thing in China is very small.

Figure 2: A crawling assassin bug (Photo by Ran Hao)

02Professional Hunter

The history of assassin bugs can be traced back to the middle Jurassic period, about 180 million years ago. Early assassin bugs were probably opportunistic predators that preyed on a wide range of prey. However, as assassin bugs have evolved to this day, in addition to those that maintain their traditional ways, many groups have developed their own unique hunting techniques, which seem very "professional".

For example, species in the Emesine Complex, which have long legs and look a bit like mosquitoes, prey on spiders. It includes three subfamilies: Emesinae, Saicinae, and Visayanocorinae. At least 39 species have been confirmed to have related behaviors. Some bugs can lure spiders by vibrating spider webs to simulate small insects, while others are more direct, with their front legs able to cut spider webs or even move on spider webs.

Some species in the subfamily Harpactorinae collect resin, sometimes colloquially called resin or glue bugs, which they apply to their forelegs to stick to prey, a method that is very effective when hunting bees and spiders. In addition, female yellow-bellied bee-hunting bugs ( Apiomerus flaviventris ) collect and store resin under their abdomens and keep it moist. These resins will be taken at any time for hunting or smearing on eggs for protection. It can be said that the role of resin has been "developed" to the extreme.

Figure 3: The assassin bug caught a bee (copyright image from the gallery, reprinting may cause copyright disputes)

03Master of Disguise

Another survival trick of assassin bugs is camouflage , which not only helps them escape the eyes of predators, but also helps them catch prey. Some assassin bugs have body colors that easily blend into the environment, and a few assassin bugs will carry things on their bodies to make themselves look more like a garbage dump.

In China, at least four species of assassin bugs are known to carry things on their backs. Some species do this when they are nymphs, that is, before they reach adulthood, such as the pale-banded assassin bug ( Acanthaspis cincticrus ); others do this when they are adults, such as the camouflage phenomenon of the double-ringed assassin bug ( Peregrinator biannulipes ), which only occurs in the adult stage. Different species carry different things at different stages of development, and can generally be divided into two categories: one is natural camouflage , which involves carrying sand and various debris on the body; the other is corpse camouflage , which involves carrying the dried carcasses of prey on the back, which increases the effect of confusing or attracting prey.

When carrying things, assassin bugs rely mainly on their hind legs, which are covered with bristles, like small brushes, and they will brush various objects onto their backs. Assassin bugs have evolved a variety of hair types to facilitate this process. For example, the pale-banded assassin bug has forked or hooked bristles to hang on to debris, and also has hollow glandular hairs connected to glandular sacs to release sticky substances.

Further experiments showed that when these burdens were removed, the mortality rate of assassin bugs would increase significantly, which also means that these "garbage" are vital to assassin bugs.

Figure 4: An assassin bug carrying an ant corpse, suspected to be a nymph of the pale-banded assassin bug (Photo by Ran Hao)

04Don’t be nervous when you encounter

Outdoors, you have a certain chance of encountering wandering assassin bugs, but please do not immediately prepare to step on them to death. This is not the right way to get along with insects. In fact, assassin bugs have their own irreplaceable functions in the ecosystem, and many assassin bugs are beneficial insects in agriculture and forestry. You don't have to avoid them deliberately. Although the bites of some assassin bugs are very painful, cases of people being bitten by assassin bugs are very rare. You can squat next to it and observe its life and behavior.

Except for the cone-shaped assassin bug, most of the bites of assassin bugs occur when they feel their lives are threatened and take defensive actions. For example, a case was reported in Mato Grosso State, Brazil, when a pair of boots were carelessly left in nature for a long time, and an assassin bug fell into one of the boots. When the owner of the boots stretched his feet to put on the shoes, he crushed the assassin bug inside and was also bitten by the assassin bug... In fact, as long as you follow two principles, the probability of you being bitten will be infinitely small:

First, don't try to kill an assassin bug that accidentally lands on you by slapping it to death; just blow it away with one breath.

Second, do not try to touch or catch an assassin bug with your hands. In fact, do not try to touch any unfamiliar insects or even other wild animals with your hands, as their counterattack may cause harm.

If you are stung by an assassin bug, you may feel pain and numbness. You can wash the wound with soapy water and disinfect it with alcohol or iodine to prevent secondary infection. Ice compress can relieve pain, but if the pain is severe, you must seek medical attention in time. The prognosis is usually good. People with allergies should carry anti-allergic drugs with them when they are outdoors and take them in time. Once severe allergic symptoms occur, such as large-area swelling, itching, urticaria or difficulty breathing, they must be sent to the hospital immediately to prevent danger.

References

Hartwig EK. 1977. Records of assassin bug species (Reduviidae, Heteroptera) reported biting man. Koedoe 20, 109-114.

Hwang WS, Weirauch C. 2012. Evolutionary history of assassin bugs (Insecta:Hemiptera: Reduviidae): Insights from divergence dating and ancestral state reconstruction. PLoS One 7, e45523.

Santos CEPD, Souza JRD, Zanette RA, Silva FJD, Strussmann C. 2019. Bite caused by the assassin bug Zelus Fabricius, 1803 (Hemiptera; Heteroptera: Reduviidae) in a human. Wilderness & Environmental Medicine 30(1), 63-65.

Singh S, Mann BK. 2013. Insect bite reactions. Indian Journal of Dermatology, Venereology, and Leprology 79, 151-164.

Standring S, Forero D, Weirauch C. 2024. Untangling the assassin's web: Phylogeny and classification of the spider-associated Emesine complex (Hemiptera: Reduviidae). Systmatic Entomology 49(1), 1-14.

Suzuki Y. 2019. Araneophagic behavior of Gardena brevicollis Stål (Heteroptera: Reduviidae): Foraging on pre-dispersal spiderlings in the spider's web. Entomological Science, doi: 10.1111/ens.12357.

Suzuki Y, Petcharad B. 2023. First record of Gardena melinarthrum (Heteroptera: Reduviidae) from Thailand with a note on its predation of an araneophagic spider. Journal of Asia-Pacific Biodiversity 16, 702e709.

Cai Wanzhi, Zhao Ping, Mi Qingshan. 2002. Camouflage phenomenon of assassin bugs. Insect Knowledge 39(4), 317-319.

Kou Fei. 2017. Camouflage behavior of the pale-banded thorn bug and the four-spotted thorn bug. PhD dissertation. China Agricultural University.

Qiao Long, Wang Chao. 2022. Stinky lady: Call me brown-winged stink bug. China Customs 6, 58.

Wang, M.X., Liu, Q. 2021. Research progress on the classification of Triatominae species using cytogenetics. Chinese Journal of Vector Biology and Control 32(1), 115-119.

Yao Kang, Deng Wangxi, Tao Jingping, Yang Zhihui, Hu Weizhi. 1984. Preliminary observation on the living habits of Diplodocus sutchus and its ability to prey on barn insects. Journal of Huazhong Agricultural University 3(1), 44-47.

Author: Ran Hao, Distinguished Researcher, Key Laboratory of Ecology and Environmental Protection of Rare and Endangered Plants and Animals, Ministry of Education (Guangxi Normal University)

Reviewer: Zhang Chenliang, deputy editor-in-chief of Museum Magazine

Produced by: Science Popularization China x Xinhuanet

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.