Species observed in temperate regions apparently have broad temperature and humidity tolerances. Although specimens are most frequently collected in moist, cool habitats, this may be a consequence of the availability of food animals. Many individuals have been collected from dry, exposed surfaces, and Bornemissza (in litt.) has evidence indicating that aCytaspecies may be restricted to the desert regions in Australia. On the other hand, Snetsinger (1956) could obtain complete life histories only at ninety per cent relative humidity between sixty and seventy degrees Fahrenheit.
Bdellids in temperate climates overwinter in all stages of development. In Kansas, the author has collected all the active stages of localCytaandBdellaspecies from leaf litter as early as February 22, and although the deutonymphal and tritonymphal stages were the most prevalent, the larvae, protonymphs, and adults were also present. Snetsinger (1956) observed that in Illinois the egg stage is the most abundant overwintering form ofSpinibdella depressa, but all stages except the larval stage were found hibernating under tree bark.
Personal observations on feeding habits were made by the use of covered stender dishes with collembola as the food source. Bdellids, when placed with collembola, move slowly until contact is made with the distal setae of the palpi. If the mite is startled, it will run rapidly backwards. If not startled, the mite will lunge at the prey, impaling it on the tips of the mouth parts. The chelicerae are rapidly and alternately extended and retracted at various angles into the body of the prey, while the chelae are opened and closed, thus macerating the tissues. If disturbed while feeding, the bdellid elevates the tip of the gnathosoma with the mouth parts still inserted in the prey, and in this fashion the mite may move away from distracting influences. When feeding is completed, the mite either goes to a secluded spot or again moves slowly about the dish.
These mites have the life history stages found in many trombidiform mites, that is, egg, deutovum, larva, three nymphal stages, and adult. Each active immature stage ends in a period of quiesence, following which the old integument is shed. Currie (1933) reported that one nymph ofBiscirus lapidariusconsumed eighteen immature clover springtails on each of three successive days, and Snetsinger (1956) reported that immatures ofSpinibdella depressarequire three or more tetranychid mites to complete each developmental stage. The latter author also found that the length of time necessary for development is partially dependent on temperature, lengthening as the temperature decreases. Development from larva to adult at ninety percent relative humidity required twenty-one to thirty days at sixty degrees Fahrenheit, but only fourteen to twenty-one days at seventy degrees.
Oviposition preferenda have not been reported; however, there is a tendency for the females to lay eggs in protected areas. In stender dishes coated with a plaster-of-paris and charcoal mixture (Lipovsky, 1953) and marked with a deep line to simulate a crack, the author observed the sites of egg deposition of four females. Sixteen spiny elliptical eggs, laid singly at the rate of one egg each one and one-half days, were deposited in the prepared crevice at the bottom of the dish, while only one egg was laid in an exposed area near the wall of the dish. In the field, Snetsinger (1956) found that large numbers of eggs were deposited during the autumn months under the basal bark of trees, probably a result of females aggregating in protected spots at the onset of cold weather.
Parthenogenesis has not been discovered in the Bdellidae. Although the forty-five specimens ofBdella tropica, sp. nov. and one hundred and forty-six specimens ofSpinibdella croniniexamined in this study were all females, this cannot be construed as proof of parthenogenetic development. In all species for which large numbers of specimens were available, there were usually many more females than males. For example, there were one hundred and fifty-six females and forty males ofBdella longicornisand ninety- two females and only four males ofBdella muscorum. The sexes were approximately equal in number only inBdellodes longirostris, of which forty-eight females and forty-four males were examined. Occasionally in small collections of two to ten specimens of the three latter species, all or most of the individuals were males. Plausible explanations for the scarcity of males, especially forB. tropicaandS. cronini, could be that the sex ratio is extremely unequal; that the males have different habitat preferences; or that they have different peaks of seasonal abundance.
Bdellids are active, fast-running mites, predaceous on small arthropods and arthropod eggs. They seem to occur in almost every terrestrial habitat where food material is available. Three investigations on the biology of these mites have been reported. Womersley (1933a) and Currie (1933) studied one species as a possible biological control agent for the clover springtail or lucerne flea (Sminthurus viridis L.) and Snetsinger (1956) studied the biology of Spinibdella depressa (Ewing).