Bats
Bats are commonly overlooked as a beneficial predator of insects. But several species live among us right here in the San Francisco Bay Area, and go out each night to make sure that there are a few less mosquitoes, not to mention garden-eating and other kinds of insects, when we wake up in the morning.
Among our most common bats are those in the Vesper family, the largest family of bats with 320 species worldwide. Vesper bats are unadorned when compared to other bats and have plain noses. The Little Brown Myotis (Myotis lucifugus) and the California Myotis (Myotis californicus) are common in Marin. They are small (roughly 3 inch long), brownish bats with narrow but relatively short ears. The Little Brown and California species differ in appearance in that the California is slightly smaller, has yellow orange dull rather than brown glossy fur, and has smaller feet.
These bats emerge from their day roosts after dusk to hunt insect prey using echolocation, the emission of high-frequency calls which echo back to the bat after bouncing off flying insects. The bats scoop the insects out of the air with their wing tips or tail membranes.
The Little Browns and California differ in habitat and prey in that Little Browns live near water and specialize in aquatic insects while California Myotis live in varied habitats and fly slow, erratically, and low over the ground hunting flies and moths. Little Browns can consume half their body weight each night, with nursing females consuming even more. Another of our common Vesper bats is the Pallid Bat (Antrozous pallidus), a lighter-colored bat that is larger than the others and has big eyes, a pig-like snout and large pointy ears. The Pallid Bat emerges late at night and flies slowly over grasslands and drier areas, capturing large insects, scorpions and small vertebrates on the ground by looking for and listening for prey rather than by using echolocation.
This bat is found in drier locations and roosts in a variety of natural structures and buildings. Vesper bats congregate in the fall to mate. Only one pup is born to a Myotis female, but Pallid bats commonly have twins. Another of our common bats is the Brazilian Free-tailed Bat (Tadarida brasiliensis), a large bat which differs from our Vesper bats in having a long tail that extends beyond the tail membrane. The males exude a musky odor from a gland on their throats. Their long narrow wings allow fast, but not precise flight. These bats aggregate in large roosts and hunt moths and other insects high over open areas at night. A single pup is born in June or July, after which the bats migrate to wintering grounds in Mexico. Bats are very long-lived relative to their size, and the Little Browns can live more than 30 years.
The Hungry Owl Project advocates using bats as another highly beneficial predator that can help solve insect pest problems. A colony of 1,000 Bats can eat 22 pounds of insects nightly. The mere presence of bats is thought to scare away insects from an area. The diet of insect eating bats consists of many crop and garden pests including leafcutters, beetles, moths, cutworms and flies, as well as mosquitoes. Bats can eat their own body weight of insects each night. Bats seldom eat beneficial insects, however. Due to the overuse of pesticides, bat populations are declining rapidly with 40% of American bat species in trouble. All of these bats roost in buildings, which sometimes results in human-wildlife conflicts. Bats have sharp teeth, and although no more likely to transmit rabies than other mammals, will bite if handled.
In Marin, contact the 24-hour hotline at WildCare (415-456-7283) if you come across an injured bat or their Wildlife Solutions Service to help with bat intrusion issues (415-453-1000 x23).
Bat Conservation International (www.batcon.org) is a great resource for the specifications for large bat houses for maternity colonies capable of housing populations sufficient to assist your farm, ranch or vineyard with sustainable pest control. HOP also has a small supply of locally built bat boxes.
