Scarab beetles are one of our largest and most divers beetle families. Most Arizonans are quite familiar with the day active Green Fig Beetle and smaller brown beetles of several genera that tend to accumulate around porch lights and are often just called June Bugs.
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| Hercules Beetle larva |
Gardeners among us usually hate the white, c-shaped, fat grubs of scarabs that live in the ground and supposedly feed on the roots of your favorite plants. Some of them might in fact do that.
But most scarabs are decomposers, and therefore very important for gardening and agriculture. Their grubs feed on dead plant material that they digest with the help of bacterial symbionts in their widely extended guts. Hence the impression that they are fat. The strong mandibles of those often very large grubs are able to break down decaying wood and leaf matter, utilize amazing amounts of material, and thus open it up to smaller decomposers, and finally fungi and bacteria. So eventually the nutrients will again be part of the garden soil and available for uptake by plants..
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| Dung Beetles of the genus Phanaeus |
Among scarabs, dung beetles have evolved to break down the feces of larger animals. The importance of this 'service' can hardly be overestimated. Obviously, they are removing waste that would otherwise pose a serious health risk. For example, dung beetles help to remove harmful pathogens like E. coli from soil. But if you consider the amount of dung that big herds of grazing animals produce, you'll understand that the mere accumulation of this dung would eventually cover so much surface that the grasses that the herds a feeding on would be displaced by a rather sterile crust of dung.
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| Canthon indigaceus and Canthon imitator form dung balls to bury their share away from competition, as food for their own offspring. |
Although there is no longer a source in the US to buy dung beetles of any type, historically, the U.S. government sponsored dung beetle introduction programs. When the local dung beetle population did not seem to be able to handle the waste of Texas' huge Cattle herds,
Digitonthophagus gazella (Gazelle Scarab) was brought in in the 1970. Of Indoafrican origin, it is now perhaps the most widespread dung beetle in tropical and subtropical pastures. (Noriega et al. 2010).
Euoniticellus intermedius was brought to Texas from Africa. Thus dung beetles from traditional feeding grounds of big herds were introduced. I do not know why dung beetles were not brought in from old buffalo grounds like the midwestern prairies, but instead from Eurasia and Africa. Maybe the introducers thought them more suitable for the Texas climate. The beetles proved invasive. They quickly spread throughout most of the southern U.S.
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Digitonthophagus gazella (Gazelle Scarab) and Euoniticellus intermedius, both introduced
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The introduced species are doing the job. They propagated so successfully that they are found all over Arizona by now. In fact, by now most larger dung beetles we find are of those two species. It is difficult to tell if this is harming the populations of endemic species that they compete with, but it is hard to imagine that they wouldn't. My impression is that the two introduced species are generalists that can deal with nearly all types of soil, and exposure. They also fly well enough to quickly move into areas were grazing is so poor that cattle may only be brought in every few years. Our endemic large
Canthon imitator, the smaller
Canthon indigaceus and the three
Phanaeus species seem be more discriminating in their choice of habitat.
