OTHER ANIMALS 667 



much larger than in some others, and are more convex than usual. 

 The particular place of oviposition is in a measure characteristic. 



The Black and White Horsefly (Tabanus Stygius Say). This 

 horsefly is very common in the vicinity of the Lake Laboratory, at 

 Sandusky, Ohio, where most of my observations on the species were 

 made. The adults appear about the 1st of July each season, and 

 are on the wing for several weeks thereafter. The females were 

 often observed biting cattle and horses, and are known to be impor- 

 tant stock pasts. The males were often seen in the marshes, on 

 grasses infested by aphides, and it is known that this sex, and occa- 

 sionally the females also, feed on honeydew which these insects 

 excrete. The species oviposits principally on the leaves of Sagit 

 taria standing in shallow water, habitually placing the eggs just 

 above the point where the petiole meets the expanded part of the 

 leaf. The precision with which this habit is followed becomes a 

 matter of much interest. 



FIELD MICE. 



While the food habits of the various species of short-tailed field 

 mice are remarkably similar, their habits and breeding differ greatly. 

 Some species prefer high and dry ground, while others live in low 

 and moist places. Some species live in forests, others in the open 

 prairies ; some burrow underground like moles, others make smooth 

 paths or trails upon its surface. The nests of field mice are compact 

 bunches of grass blades and other dry vegetable fibers, and are ad- 

 mirably located in respect to drainage. Most surface nests are for 

 shelter only as for the most part the young are born in underground 

 nests. 



The breeding season includes most months of the year, except 

 midwinter in cold latitudes. Some species normally produce from 

 two to four litters a year, while others produce from four to eight. 

 Period of gestation probably about twenty days. The common 

 meadow mouse of the United States is one of the most prolific of our 

 species. Estimating the normal increase at six young with four lit- 

 ters in a season, without making allowances for any loss, a single 

 pair would produce in five seasons nearly 1,000,000 individuals. 



In summer the chief food of field mice is green vegetation and 

 unripe seeds of grain and grasses, later in the season ripe seeds be- 

 come an important diet. In winter bulbous and other roots with 

 stored seeds are largely eaten. During cold weather young forest 

 trees and young apple orchards suffer from attacks of mice. Black- 

 berries, raspberries, currants, grapes, strawberries, etc., are often badly 

 damaged by girdling done by field mice. In fact, sometimes whole 

 plantations are ruined. Field mice destroy bulbs, perennial plants, 

 woody shrubs, and ornamental vines. Neglected young apple or- 

 chards are sometimes almost completely ruined, the damage in fre- 

 quently very considerable. 



Fortunately for the farmer there are several natural igencMl 

 that tend to hold the mice in check. Long and severe cold winters 

 with dry summers seem to be unfavorable for their production. Tim 

 chief natural enemies of field mice are: (1) mammals both wild and 



