Dung beetles offer the ideal study system for extreme weapon evolution.

Evidence

A second strategy adopted by many dung beetles is tunneling. Females of these species fly into dung and immediately begin to excavate burrows into the soil below. Once they’ve dug sufficiently deeply—a foot to a yard, depending on the species—they begin pulling pieces of dung down into the tunnels to stash them away from the other dung-feeding insects above. … Males of tunneling species often have horns. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 222 (#expands, via linked claim)

Such is the reality of extreme animal weapons. Brutal and beautiful, extreme weapons have cropped up repeatedly during the unfolding of the history of life. All told, some three thousand species now wield them. That’s a drop in the bucket considering there are 1.3 million described types of animal, but it’s a collection packed with remarkable creatures. Early champions include the horns of triceratops, titanotheres, and trilobites, the tusks of mammoths and dolphins, and the racks of Irish elk. Today, extreme weapons are wielded by walruses, antelope, whales, crabs, shrimp, beetles, earwigs, plant bugs, and flies, to name just a few. The weapons themselves can be matted hair, bone, teeth, or chitin, and they take any number of different forms. Some, for example, are overgrown versions of an existing structure, like a tooth or a leg. Others appear to have arisen de novo, as new bumps or knobs that became so large they formed their own distinct structure. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 15 (#expands, via linked claim)

Eyes in male stalk-eyed flies sprout like lollipops from the sides of their heads, giving these flies an uncanny resemblance to miniature sets of barbells. Males in some species have absurdly long eyestalks, while males in very closely related species do not. As with dung beetles, we can explain this variation by looking closely at the natural history of each stalk-eyed species. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 253 (#expands, via linked claim)

Categorization

• XREF: connects to: Extreme weapons evolved independently across roughly three thousand species — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 15; Tunneling dung beetles guard burrow entrances and evolve horns; rollers do not — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 222; Variation in animal weapon size is explainable by species ecology and behavior. — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 253

Related

• Extreme weapons evolved independently across roughly three thousand species (similarity 0.90)
• Variation in animal weapon size is explainable by species ecology and behavior. (similarity 0.88)
• The same three ingredients trigger weapon evolution across wildly divergent animal clades (similarity 0.85)
• Tunneling dung beetles guard burrow entrances and evolve horns; rollers do not (similarity 0.85)
• Animal weapons evolved to extremes far beyond practical size (similarity 0.83)
• Tunneling behavior predicts horn evolution in dung beetles (similarity 0.83)
• Extreme weapons across many insect species stunt eyes, wings, antennae, and testes (similarity 0.82)
• Competition for reproduction drives evolution of nature’s biggest weapons (similarity 0.82)
• Dung beetle horns evolved and were lost repeatedly across their history (similarity 0.82)
• Extreme male weapons evolved independently at least eleven times in vinegar flies (similarity 0.81)
• No ball-rolling dung beetle species has evolved horns despite constant fighting (similarity 0.81)
• Extreme weapon size is relative to body size, not absolute (similarity 0.81)
• Identical triggers drive extreme weapon evolution across wildly unrelated clades (similarity 0.81)
• The evolutionary drivers of animal weapons also explain human weapon elaboration. (similarity 0.81)
• Beetle horns can be impressively large yet nearly cost-free to produce and use (similarity 0.80)

Broader Connections

• Tunneling dung beetles guard burrow entrances and evolve horns; rollers do not #expands (0.70) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 222
• Extreme weapons evolved independently across roughly three thousand species #expands (0.55) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 15
• Variation in animal weapon size is explainable by species ecology and behavior. #expands (0.50) — Emlen, Douglas J, Animal Weapons_ The Evolution of Battle, 253