Brachinus fumans

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Geographic Range

Bombardier beetles can be found on most continents around the world, but the particular species chosen for this report is found only in North America. Bombardier beetles of all types generally live in temperate zone woodlands or grasslands (Isaak 1997; Salleh et al. 1999).

Habitat

Bombardiers can inhabit a fairly wide variety of environments as long as there is sufficient moisture to allow for good places to lay their eggs. Bombardier beetles of all types generally live in temperate zone woodlands or grasslands (Isaak 1997, Salleh 1999).

Physical Description

Like all members of the insect order Coleoptera, the bombardier beetle has two elytra (sheaths) over its wings, although the wings themselves are considered vestigal in the American species, and rather useless for flying. To compensate for this inability to escape by flying away from predators, the beetle possesses a rather interesting apparatus for defending itself against predators, which will be elaborated on later. All of the other characteristics of insects in general (six legs, two antennae, body segmented into head, thorax, and abdomen, etc.) are present (Isaak 1997).

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Reproduction

Any place will do for a ground beetle to lay its eggs, so long as it's out of the way of most predators, but not too far away from a good food source. Small underground tunnels or cracks in rotting wood are viable places, as are the decomposing remains of other living things (which quite often serve as the food source.) When the egg hatches, it goes into the larval stage, where it begins alternately taking in nourishment from the food source and occasionally molting. After it sheds its skin for the last time, it metamorphoses into a pupa, the stage at which the juvenile looks most like the adult which it will eventually become. At the end of the pupal stage, the pupa sheds its skin and a new adult bombardier beetle emerges. Ground beetles tend to live for several weeks, during which they have ample opportunity to mate and pass on their genes (Shetlar 1988).

Behavior

The main reason the bombardier beetle is so notable is due to the two small glands located near the end of its abdomen. One gland produces hydrogen peroxide, one gland produces hydroquinone. The two chemicals are mixed in what is evocatively called the "explosion chamber" and have two enzymes, catalase and peroxidase, added to them. These enzymes speed up the reaction to a level where the beetle can make an audible "pop" as it ejects the now-boiling chemical stream at whatever unlucky predator happened to disturb it. Added to this, the beetle can rotate the end of its abdomen 270 degrees in any direction, which allows for an impressive "firing range." In effect, the beetle can spray in whatever direction the predator comes from, a decided advantage (Dawkins 1985; Eisner 2000; Salleh 1999).

Food Habits

A member of the family Carabidae, more commonly known as the ground beetles, the bombardier beetle quite naturally shares some of the habits of its family, and like most other ground beetles tends to come out at night to prey on smaller insects. Unlike most other ground beetles, however, the bombardier is rather gregarious, so when not wandering around looking for food (usually during the day) it will congregate with others of its kind in dark, damp places such as hollow logs (Eisner 2000; Shetlar 1988).

Economic Importance for Humans: Positive

This species, like nearly all the species in the family Carabidae, is a predator, and eats a number of other insects that are agricultural pests. (Shetlar, 1988)

Conservation Status

Most of the scientific research done on the beetle has focused on its defense structures, so the question of how it fits into the larger ecological picture in its particular environment is not very well known. It is widely distributed across North America, though rarely found in large numbers.

Other Comments

The defensive structures of the bombardier beetle have been the subject of debate between creationists and evolutionary biologists. Some "creationists" have claimed that the complex defensive spray mechanism of the bombardier beetle is too complex to have evolved naturally. They say such a thing must have been created by a higher intelligence. Evolutionary biologists have discredited this argument, and have presented reasonable explanations for how the structures could have evolved from simpler chemical glands. (Dawkins, 1985; Isaak, 1997)

Contributors

Ezra Poetker (author), University of California, Irvine, Rudi Berkelhamer (editor), University of California, Irvine.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

native range

the area in which the animal is naturally found, the region in which it is endemic.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

References

Dawkins, R. 1985. The Blind Watchmaker. London: W.W. Norton.

Eisner, T. 2000. "A Shot in the Dark" (On-line). Accessed October 12, 2000 at http://www.thebookery.com/Bookpress/article.cfm/10.4/177.Eisner7615.html.

Isaak, M. 1997. "Bombardier Beetles and the Argument of Design" (On-line). Accessed October 12, 2000 at http://www.talkorigins.org/faqs/bombardier.html.

Salleh, A. 1999. "No place to hide" (On-line). Accessed October 12, 2000 at http://www.abc.net.au/science/news/stories/s44387.htm.

Shetlar, D. 1988. Beetle. USA: World Book Encyclopedia, Inc..