THE FOREST CATERPILLAR HUNTER, Calosoma sycophanta, IN VIRGINIA

By Arthur V. Evans

In July of 2008, while conducting a beetle survey of the Bull Run Mountains Natural Area Preserve in Fauquier and Prince William counties in Virginia, I found numerous metallic green elytra scattered along a foot trail winding through an oak woodland on a west-facing slope. The area had been heavily infested with larvae of the gypsy moth, Lymantria dispar, as evidenced by thousands of larval exuviae and pupal cases that festooned the trunks of oaks and other hardwood trees.

At first glance, I thought the beetle remains were those of the indigenous caterpillar hunter or fiery searcher, Calosoma scrutator, a common, brightly colored, and widespread carabid beetle found in the mountains and lowlands of Virginia. Closer inspection revealed that the elytra were much brighter and more yellow than those of C. scrutator and lacked the characteristic coppery red margins.

Further searching in the area produced a very fragile, yet nearly intact specimen ensnared in an abandoned spider web. The pronotum of this specimen was mostly black with metallic blue along the margins, rather than bluish with violet or coppery yellow green borders typical of C. scrutator. Of the five other species of Calosoma known in Virginia, only C. wilcoxi has entirely metallic green elytra, but it is smaller and much duller than either C. scrutator or the silk-wrapped remains in question. (Figure 1).

Figure 1. The Virginia species of Calosoma (from top to bottom, left to right): C. calidum (F.), C. externum (Say), C. frigidum Kirby, C. sayi Dejean, C. scrutator F., C. sycophanta (L.), and C. wilcoxi LeConte. The scale bar equals 5.0 mm. © 2009, Chris Wirth.

I soon realized that what I had in my possession were the remains of a European species, the forest caterpillar hunter, C. sycophanta. Long known as an important predator of gypsy moth larvae in France, 4,046 of these beetles were imported into the United States between 1905 and 1910, most of which were released in New England to combat outbreaks of two European species of lymantriids: the gypsy moth and the browntail moth, Euproctis chrysorroea.

In the United States, the forest caterpillar hunter is established in Connecticut, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Washington. They have been released in Delaware, Michigan, Washington, and West Virginia, but they have yet to become established in these states. In spite of releases on Vancouver Island, British Columbia, Quebec, New Brunswick, and Nova Scotia, the forest caterpillar hunter does not appear to be a permanent resident in Canada either.

Both the adults and larvae climb trees to attack and eat caterpillars and pupae of gypsy moths and other species. Adult males are more likely to be found on tree trunks, while females tend to remain on the ground. Based on observations in the laboratory and in the field, both sexes are active day and night. Males tend to be more conspicuous as they spend most of their time actively searching for mates. The more secretive females spend much of their time buried in the soil and hidden among leaf litter to feed and lay eggs.

Adult activity coincides with the larval activity of the gypsy moth. Beetles emerge from their overwintering sites in June to search for prey and mates, although some beetles may remain dormant for up to two years. Although adults are strong and agile fliers capable of leaving their overwintering sites behind to search for high populations of caterpillars, their appearance at new outbreaks of gypsy moths is by no means certain. In fact, beetles released as part of biological control programs often remain near their release site.

Forest caterpillar hunters will attack a variety of other caterpillar species, but are most abundant where populations of gypsy moth caterpillars are high. They remain active for about a month, re-enter the soil, and remain there until the following spring.

Adult predation is not this species’ primary impact on gypsy moth populations. It’s greatest impact is through larval production and the voracious appetites of the beetle’s larvae for mature caterpillars and pupae. The ability of adult beetles to reproduce is directly dependent upon the availability of high densities of gypsy moth caterpillars, especially since females require sufficient protein to ensure successful development of their eggs.

Eggs are laid in the soil beginning in early July and hatch in 4-7 days. The larvae climb trees in search of caterpillars and pupae. The remains of pupae attacked by beetle larvae have characteristically large and jagged holes. Mature beetle larvae seek pupation sites in the soil. The entire life cycle, from egg to adult, takes about seven weeks. In Connecticut, adults are known to live three to four years.

Anecdotal evidence suggests that forest caterpillar hunters are potentially important predators of gypsy moth larvae and pupae, but there is still much to learn. Nearly all of the information on the ecology and behavior of C. sycophanta was gathered during the brief period of adult activity that coincides with gypsy moth outbreaks, but little is known about the ecology of this species between outbreaks.

Many thanks to Chris Wirth for the wonderful color plate. This essay is excerpted from Evans, A.V. 2010. The forest caterpillar hunter, Calosoma sycophanta, an Old World species confirmed as part of the Virginia beetle fauna (Coleoptera: Carabidae). Banisteria [2009] 34: 33-37. The full article is available at http://fwie.fw.vt.edu/VNHS/banisteria/banisteria.asp.

©2010, A.V. EVANS

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10 Responses to “THE FOREST CATERPILLAR HUNTER, Calosoma sycophanta, IN VIRGINIA”

  1. Wow, what a looker! I don’t know if I should be happy that such a beautiful beetle has been added to the North American fauna, sad that it might potentially displace native species, or puzzled by the arboreal larval habits of this “ground” beetle.

    Superb plate – is it a composited of extended-focus images? The clarity on the full-sized version is outstanding.

    Thanks also for the link to Banisteria, although I note with disappointment that among the very few titles that do not contain links to the article are the two that I am most interested in seeing. Any chance I could acquire these somehow?

    Number 22, 2003
    Beetles of the Genus Anthophylax in Virginia (Coleoptera: Cerambycidae: Lepturinae) – Richard L. Hoffman.

    Number 20, 2002
    Thirteen Additions to the Known Beetle Fauna of Virginia (Coleoptera: Scirtidae, Bothrideridae, Cleridae, Tenebrionidae, Melyridae, Callirphidae, Cerambycidae, Chrysomelidae) – Richard L. Hoffman, Steven M. Roble, and Warren E. Steiner, Jr.

    • Arthur Evans Says:

      Ted,

      Chris Wirth can fill you in on the details of the plate. I do know that it is a composite. As for the Banisteria articles, you might try contacting Richard Hoffman to see if he has pdfs of those papers. If not, I would be happy to scan those papers for you and send them along.

      ART

  2. Very interesting! I did not know that the larvae could be arboreal, too. Amazing. Did not see either adults or larvae in western Massachusetts, but not many gypsy moths, either, for that matter.

  3. Candace Ramseur Says:

    These beetles are beautiful. However, they have invaded our home. When we catch them, they emit a terrible stink and we have been reading that their bite is not pleasant. One fell out of a pair of pants that had been hung to dry. I am uncomfortable living with them in my house. Do you have any suggestions? We live in South Carolina and I found nothing on the Clemson Extension site. Hope you can help.

    • Do you have a picture of one of these beetles? I suspect that it is a another species, Calosoma scrutator and that it was a single beetle looking for a warm, dry spot to spend the winter.

  4. Nicole Lewis Says:

    I live in Southeastern Massachusetts and I would love to buy some of these. Over the past few years our trees have been destroyed by Gypsy Moths and my husband believes they are spreading to my rose bushes. I am buying some ladybugs for my roses but I would love to treat my trees. It is heartbreaking to see trees with no leaves and more trees with huge holes in the leaves!

  5. LaDonna Sherrell Says:

    I have been invaded by hundreds of these beetles. We have had a great spring this year and the trees, rose bushes, garden, and lawn have been better than even in the 30 yrs we’ve been here. But you can have these bugs. After reading up on these bugs, it all makes sense why we have no moths, and many other lack of bugs around our yard. But we can’t have any porch lights on, etc. or these bugs are all over, coming in the house. We can’t go outside at all in the evening on our porch. We don’t need so many, and the smell, yuck. I would love to give some farmers who need them to them. Any suggestions on what to do? I think I’m going to call the agriculture dept. at ATM college that is 15 miles away from us.

    • LaDonna Sherrell Says:

      I forgot to mention, I live in east Texas about an hour east of Dallas, TX. Those Forest Caterpillars have made it to Texas. And yes it is the Forest Caterpillar Hunter.

  6. Godfrey Nalyanya Says:

    I am an entomologist with Rentokil/Ehrlich Pest Control and today we had quite a number of calls from our clients who are experiencing invasions of these beetles. These has not happened before. Are these beetles changing their behavior and invading structures? I would be interested to know which species is currently invading buildings around the Northern Virginia Area. I also heard they are covering buildings in the St. Louis MO area. Would they be the same species?

    Thanks.

    • The species that is common here in VA at the moment is Calosoma wilcoxi. Hardly a pest, they are devouring the bumper crop of fall cankerworms. Both insect seem to be on the wane now here in the Richmond area.

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