Metrius contractus on a leaf feeding. Image taken by and used with permission from Sarah Crews.

Habitat, Geography, and Interactions

Metrius contractus on wood. Image taken by and permission to use from Mark Leppin.Metrius contractus can be found crawling in the forests of California and in many other parts of the United states. Metrius contractus is actually the only American species belonging to the genus Metrius (Eisner et al. 1977, Eisner et al. 2000).  They can also be found in Europe and other parts of North America (Agosta 1996).  The bombardier beetle dwells in temperate grasslands and temperate woodlands because it is important for the beetle to have access to decomposing matierals for its reproduction and for its overall survival due to the high amount of moisture found in these kinds of environments (NWF 2013).  Temperate grasslands have many kinds of leaves and grasses that offers a great place of protection for Metrius contractus (Campbell et al. 2008).   Bombardier beetles can surprisingly be found in deserts and savannas (UTEP 2007); however, there is a preference for the beetle to be in a temperate climate so it can be exposed to a highly moisturized environment. 

They are primarily active during the night (Agosta 1996).  This is the optimal time for the beetle to search for food, such as tiny insects (UTEP 2007).  Bombardier beetles consume an interesting diet, including larvae of moths.  They also eat the larvae of other beetles (Agosta 1996).  To learn more about beetles, check out Insect World!

A close up of Metrius contractus. Image taken by and permission to use from Mark Leppin.The bombardier beetle is not exactly the most friendly beetle thanks to its ingenious chemistry.  Since this clever beetle has evolved an excellent strategy in chemistry, the jet stream emitted from the posterior end of the beetle makes the task of scaring predators off a lot easier (Eisner et al. 1990).  The beetle attacks many kinds of species, such as ants and frogs (Eisner et al. 1977).  Interestingly, when a bombardier beetle sprays at a human that is holding the bug, the spray causes the skin to tan due to the complex chemicals that make up the spray (Eisner et al. 1977).  The beetle also emits a strong and rather unpleasant smell when it sprays to defend itself (UTEP 2007).  While it may be proficient in protecting itself, the bombardier beetle is slow to get away from predators, hence why its spray is so helpful (Eisner et al. 2000).  This is also why it is important for bombardier beetles to live in temperate grassland environments.  This type of environment provides a place of protection for the beetle if it needs to avoid predators (NWF 2013).

Metrius contractus in temperate grassland climate. This beetle needs an area with a high amount of moisture. Image taken by and permission to use from Mark Leppin.

While it may seem that Metrius contractus is invincible because of its potent chemical spray, there are other organisms such as the Orb-weaving spider that may successfully attack and capture the beetle to feed on it (Eisner et al. 1976).  The talented spider does so, according to Eisner (Eisner et al. 1976), by first attacking the beetle without hesitation.  This is very important for the spider since Metrius contractus cannot proficiently avoid predators since it moves very slow.  The spider then creates a silky layer around the beetle, which protects the spider from the beetle's defensive tactic (Eisner et al. 1976).  Experiments performed by Eisner (Eisner et al. 1976) revealed that the spider would occasionally back away from the beetle since the beetle does discharge a very toxic spray; however, the beetle was no match for the spider, and the spider continued to create its silky trap.  The spider would then bite the beetle, secrete its poisons, and eat it (Eisner et al. 1976).   

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