The Firefly Forest

Robber Flies (Family Asilidae) are medium to large flies that prey on other flies and insects. These predatory flies are usually seen either waiting on low perches in open, sunny areas or buzzing around as they look for prey. I observed this female Robber Fly below embracing a captured Eristalis Fly (Eristalis sp.) in Arizona's Santa Catalina Mountains. Eristalis Flies are bee-sized, so one of these plump, flower-loving flies would make a good-sized meal for a hungry Robber Fly.

As this photo shows, Robber Flies are quite capable of handling large prey, and they will even take on large, dangerous prey like bees and wasps. However, unlike bees and wasps, Robber Flies do not sting, and the "stinger" on this Robber Fly is actually a harmless ovipositor that she uses for laying eggs. Although they do not sting, Robber Flies do bite and their saliva contains neurotoxins to quickly immobilize prey and proteolytic enzymes to dissolve its internal organs so that they can later be easily sucked out. The proboscis of a Robber Fly is specialized for stabbing and sucking, and after one of these flies captures something, it will return to a perch in its territory to suck out its liquefied meal.

Robber Flies are highly beneficial insects because they prey on a wide variety of pest flies, so I rescue any that get trapped in my house or swimming pool. Although they don't attack or bother humans, Robber Flies can bite quite painfully, so do not capture or pick up these flies with your bare hands.

Although some species of Robber Fly appear bee-like, most species of Robber Fly have a characteristic elongated shape, almost like that of a short, fat dragonfly. Robber Flies have a single pair of powerful wings, spiny legs that aid in grasping prey, a heavily bearded face, and large compound eyes that give them excellent vision for spotting prey.

Variegated Squirrels (Sciurus variegatoides) are large, arboreal squirrels found in tropical woodlands and scrublands from southern Mexico to Panama. Throughout their range, Variegated Squirrels are amazingly variable in their coloration. We observed these Variegated Squirrels in Alajuela, Costa Rica, and their gray, rufous, and white colors were typical of those found in this area. A white and black subspecies is also found in Costa Rica, but we did not observe them.

Despite their widely varying colors, Variegated Squirrels can generally be identified by their long, bushy but flattened, white-frosted black tail, dark back, and light patch behind the ears. In Costa Rica, the Red-tailed Squirrel (Sciurus granatensis) is similar with its dark back and rufous undersides, but it has a rufous tail unlike the Variegated Squirrel.

Variegated Squirrels feed mainly on fruit and nuts, which are plentiful in tropical forests, but they will also feed on vegetation as well. The Variegated Squirrel above was atop a towering stand of bamboo nibbling on the tender young leaf buds and twig tips. Amazingly, this agile, arboreal squirrel was not at all bothered by the slenderness of the stems at this height, and it fearlessly leapt from slender stem to stem as it searched for the tastiest twigs and buds.