Tuesday, September 2, 2014

Sundew Assassin Bugs: Zelus

Your garden is full of amazing predators, easily overlooked among the foliage and flowers. No matter where you live in the U.S. and southern Canada, save perhaps for the northern Rocky Mountains, you probably have sundew assassin bugs of the genus Zelus lurking in the yard. These leggy insects move slowly about, or wait in ambush for potential prey.

Zelus luridus female, Colorado

There are currently five recognized species of Zelus north of Mexico, most with wide geographic distributions. Few are readily identifiable to species just by looking at them, but common ones include: the lovely green Zelus luridus with a sharp spine on either side of its thorax; the bright red and black Milkweed Assassin Bug, Z. longipes found in the southeast U.S.; and the non-descript Z. tetracanthus with its four small "knobs" across the top of its thorax. The Leafhopper Assassin Bug, Z. renardii, is common in the southwest U.S. and has been entertained as a potential biocontrol agent for pest reduction in agricultural settings.

Zelus longipes, South Carolina

Sundew assassins get their common name from the unique physiology that allows them to catch prey. While ambush bugs have extremely muscular front legs that snap shut on prey with stunning force, sundew assassins look like the 90-pound weakling by comparison. Their appendages are thin and seemingly delicate or flimsy. The tibiae ("shins") of the front legs (and to some degree the middle legs) are densely covered in short hairs, and this is part of their secret weapon.

Zelus tetracanthus, Colorado

Special glands in the exoskeleton of the legs secrete a glue-like material that that the insect intentionally smears over those hairs. This creates a sticky layer that small prey cannot escape from once the assassin grabs them. The prey-catching scenario is analogous to the insect-eating plant known as the sundew, which inspires the name "sundew assassin bugs."

When they hatch from the egg, nymphs do not have the ability to produce the glue they need. No matter, mom has covered the egg cluster in sticky goo to help repel egg parasites like tiny wasps, and the nymphs simply wipe their "arms" along the base of the egg mass to gather some glue (Weirauch, 2006).

Zelus luridus nymph, Colorado

Nymphs go through five instars (an instar is the interval between molts) on their way to adulthood. They are noticeably larger after each molt, with wing pads evident in the last couple of stages.

Zelus hatchlings

The egg mass reminds me of a tiny crème brûlée, but perhaps I need to eat lunch and return to finish this post later....I was delighted to stumble upon a couple of egg masses in the act of hatching at the Cheyenne Mountain Zoo here in Colorado Springs back on July 21. It seems remarkable that such long-legged creatures could be packaged in such small vessels.

Zelus hatchlings

There are at least two generations annually here along the Front Range in Colorado, probably three or more generations in southerly latitudes. I notice nymphs of Z. luridus in spring, so it is likely that winter is passed in the egg stage.

Zelus species range from 14-21 millimeters in body length as adults, and are relatively easy to recognize with their slender build, long legs and antennae, and diurnal period of activity. They are largely arboreal, so you will find them mostly on foliage and flowers of trees, shrubs, and herbs.

Zelus renardii, Texas

Assassin bugs in general are indiscriminate predators of other insects, and Zelus is no exception. So, while they will dine on leafhoppers, small caterpillars, and other pests, they will also capture beneficial insects such as small bees.

Despite our tendency to classify insects as "good" or "bad" for our own selfish reasons, sundew assassin bugs should be welcomed for the benefits they provide in occasional pest control, and their unique behavior and "personality," if I dare use that word for an invertebrate.

Zelus luridus male, Colorado

Sources: >Valerie. 2014. "Reduviidae ~ Assassin Bugs," Austin Bug Collection.

Weirauch, C. 2012. "Taxonomic Revision of Zelus Fabricius," Heteropteran Systematics Lab @ UCR
Weirauch, C. 2006. "Observations on the sticky trap predator Zelus luridus STÅL (Heteroptera, Reduviidae, Harpactorinae), with the description of a novel gland associated with the female genitalia," Denisia 19, zugleich Kataloge der OÖ. Landesmuseen Neue Serie 50 (2006), 1169-1180.
Wolf, Klaus Werner and Walton Reid. 2001. "Surface Morphology of Legs in the Assassin Bug Zelus longipes (Hemiptera: Reduviidae): A Scanning Electron Microscopy Study With an Emphasis on Hairs and Pores," Ann. Entomol. Soc. Am. 94(3): 457-461.

24 comments:

  1. Thanks for the post! I believe I now know the name of these cute little green bugs I've experienced that pack quite the painful bite!

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    1. You're welcome, Ron! yes, assassin bugs in general can give a painful bite in self-defense. The worst bite I've ever experienced was from another kind of reduviid.

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  2. Eric, any idea how long it takes for Zelus eggs to hatch? I collected and kept a female Z. renardii in a small jar for a few days and then let it go. While in the jar, she laid eggs that I did not notice. After what seemed like just a few days I noticed the nymphs crawling all over in the jar.

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    1. I do not know the answer to that. I suspect it varies a bit, from species to species and region to region, but I imagine it takes a week or two for the eggs to hatch.

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  3. Hi Eric, I found two of these little guys in my apartment (I have many house plants) do they pose any danger to humans or pets? Do they carry any viruses?

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  4. Just saw what I thought are my first samples of this species after more than 20 years in this area but saw two on the same day. Funny how that works.

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  5. I found a Zelus Renardii nymph crawling on my bed on the second story. Is there a chance that it emerged from eggs laid in my house? Also, what do Zelus Renardii nymphs eat?

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    1. Not likely that eggs were laid indoors. Could have fallen off a tree, been blown in....Nymphs feed on any insect they can overpower.

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    1. That is a medical question and I am unqualified to answer it. Seek a physician if you experience symptoms out of proportion to the bite (beyond normal localized pain, inflammation).

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  7. is this ok to have as a pet my son caught one and we thought it was a baby mantis. it just shed and we have been giving it ants to eat or should we just let it go?

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    1. Yes, it is fine to keep as a pet, but don't feed it ants, especially after it has just molted. Ants can kill it! Feed it aphids, leafhoppers, and other small insects that cannot bite or otherwise defend themselves easily.

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  8. I found one in my kitchen, I think, but it doesn't have any wings. It looks like the pictures though. is it possible that it is one?

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    1. Quite possible indeed. Nymphs, which are probably already evident in southern latitudes by now, do not have wings.

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  9. Hello Bug Eric! I have found so many Zelus luridus coming for me in my house. I keep putting them back outside. They are very gentle and I have not been bit, but do they carry any disease I should be concerned about? I keep finding them just crawling about on me and let my daughter handle one thinking it was a baby praying mantis. Have caught and released about ten in last few weeks! I would feel better if I knew they did not carry the changas disease. So hard to tell from the internet. Ty! Lisa :)

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    1. No, this is not a disease-carrying species. I have a post about kissing bugs (two, actually). Just click on the "biting bugs" category near the top right of this page.

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  10. Hi, I found three just kinda chilling under my mattress. They were really slender and skinny. I thought it was a stickbug but one of the other pictures looked more accurate. I live in Missouri. Should I be concerned?

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    1. Odd place to find them, so I might want to take a specimen to a local entomologist at a university, natural history museum, or even the public health department (vector control will have at least one entomologist).

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    2. I did that and found out they were wheel bug nymphs. I guess they got trapped because I tolk out my ac unit

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    3. They are also ( I read) predators of bedbugs and will be found around especially under beds where bedbugs or other small crawlies find refuge from light and commotion

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    4. No, these species of assassin bugs do NOT come indoors. You are thinking of the Masked Hunter, Reduvius personatus (my first "True Bug Tuesday" post).

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