PLANTS | ANIMALS | ECOLOGY | FUNGI | GEOLOGY | GARDENING | TOOLS
MEXICAN PLANTS & ANIMALS HOME
Excerpts from Jim Conrad's
Naturalist Newsletter
Entry dated August 12, 2023, issued from near Tequisquiapan, elevation about 1,900m (6200 ft), Querétaro state, MÉXICO
(~N20.57°, ~W99.89°)
DUNG BEETLES
Now during a long-term drought growing increasingly severe month by month, dung beetles, or tumblebugs, emerge only after the rare rain. After a brief shower when the ground doesn't soften, the next day they're not to be seen, but if there's enough rain to soften the ground many emerge, and several might be seen clustered around a single ball of cow or sheep poop, as shown above. Many dung beetle species are known, so to identify them attention to details must be paid. Above, field marks to note include their size, 14-15mm long (~9/16th inch), all black color with no iridescent green, purple or other sheen, and no hairs.
With such large, powerful-looking front appendages with fingerlike spurs at the tibia's base, it's easy to guess that this species digs in the ground. Notice that the protective plate atop the head, the clypeus, has slits where one might expect eyes. In some species with such slits, the compound eyes can be seen through the slits, but in this species the slits are so narrow that one wonders whether the beetle sees much. It's true that as they work often they bump into things. Often the clypeus bears one or more projections, like rhinoceros horns, but this species has none. Similarly, some species have humps on their "backs," or pronotums, immediately behind the head, but this species has none. Often the hard wing covers, the elyta, is furrowed with many shallow, slender lines running longitudinally, but this species doesn't. Our species' body is a particularly simplified and streamlined one.
Numerous species develop branched antennae such as the above, but some don't. Those antennae are fairly typical.
Most dung beetles belong to the Scarab Beetle Family, the Scarabaeidae, of which over 30,000 species are recognized worldwide. To begin my search for our beetle's identity, I used DiscoverLife.Org's online identification key for the Scarabaeidae. By keying in our beetle's length, single body color, and its absence of head projections and hairs on its back, the possible identities were narrowed down to four species, of which one looked quite different from ours. The other three were similar but not identical, and all belonged to the genus Canthon.
On the occurrences map at the GBIF database for the genus Canthon, when I checked to see if Canthon species have been documented in the semiarid part of our upland central Mexico region, I saw that one species has been documented from here, and pictures of it looked exactly like ours. That was CANTHON HUMECTUS, sometimes known as the Humid Dung Beetle, but that's just a translation from the binomial and not really a common name. The species occurs from the most arid parts of the US southwestern states south through most of Mexico.
The 2014 study by Ilse J. Ortega-Martínez and others entitled "The Role of Canthon humectus hidalgoensis (Bates) (Coleoptera: Scarabaeidae) in Dung Removal from a Cattle Pasture," not only advises us that our beetle probably is the subspecies hidalgoensis, since Hidalgo state lies just a few kilometers to our east, but also it reveals a great deal about our beetle's life history, and its ecological role.
That work tells us that our beetle works during the day, making dung balls which are rolled from cow patties to other places. Individual beetles do this to have something to eat, and pairs do it for food and nesting. For nesting, the male rolls the ball by pulling it with his hind legs. During this process, the female is attracted by the male's pheromones, gets atop the ball and helps in the rolling. The male buries the dung ball, and the female transforms it into a brood ball by laying eggs in it.
This treatment of dung isn't the same for all species. Some kinds of dung beetle live in the dung and eat it, but don't make balls. Some beetles roll balls but don't bury them. A more general survey of dung beetles appears on Wikipedia's Dung Beetle page.
from the April 21, 2007 Newsletter issued from Sierra Gorda Biosphere Reserve, QUERÉTARO, MÉXICO
FIVE TUMBLEBUGS IN A ROW
I think more cows and burros use the trail from Cocos to the valley floor than people, for there was plenty of manure on it, fresh and dried-out. One pile was so fresh that tumblebugs were still working on it. I got down on my belly and took the best picture I could of one, though my camera isn't much for close-ups. You can see a manure-encrusted tumblebug (on the ball's right) using his hind legs to push the ball up the trail.
Tumblebugs are scarab beetles -- members of the insect family Scarabaeidae. The ones I've seen have all been thick-bodied, black beetles. When they find poop they mold it into balls, roll the balls away for eating, and maybe for laying their eggs in them. When the eggs hatch, the kids find themselves surrounded by food. Lots of tumblebug species exist, and some specialize in tumbling pre-formed, pellet-like droppings of rabbits, sheep and deer.
On my tumblebug trail, five tumblebugs in a row were rolling their balls up the path, one behind the other, about 15 inches apart, and it was a funny thing to see. The trail was fairly steep and occasionally a ball got out of control and rolled backwards, carrying its tumblebug with it. And two balls each were being pushed by two bugs instead of one. Sometimes the two more or less canceled out one another's efforts, but other times one bug hung on while the other tumbled it with the ball. In fact, in my picture if you look beneath the pushing bug you can see a second tumblebug, upside-down, basically just in the way. These particular tumblebugs make manure-tumbling seem a pretty disorganized, grungy business.
Still, some tumblebugs are elegant. The sacred Scarab of the ancient Egyptians is a dung beetle native to Mediterranean countries.