1984] 
Wise — Phenology of filmy dome spider 
283 
structure resulted from poorer survival of the later egg sacs in 1982 
compared to 1981, in addition to environmentally caused differ- 
ences in developmental rates of hatchlings. These suggestions are 
speculative, as no data exist from which the causes of this particular 
yearly difference can be deduced. 
Variable Phenologies in Other Spiders 
Environmentally induced variable phenologies occur in other 
spiders (e.g. Dondale 1961, Almquist 1969, Toft 1976, 1983). Fre- 
quently this variation is correlated with differences in length and 
average temperature of the growing season, either between years or 
along latitudinal and elevational gradients. However, most exam- 
ples involve shifts not between univoltine and bivoltine patterns, but 
between annual and biennial life cycles. In fact, the occurrence of 
two generations per year has not been reported often for spiders. 
Juberthie (1954) concluded that several species he studied had bivol- 
tine life cycles, though his evidence came solely from laboratory 
rearings. At least one of the species that he studied apparently com- 
pletes only one generation per year in nature ( Enoplognatha ovata; 
Seligy 1971). However, examination of areas warmer than those 
studied by Seligy might reveal a biannual phenology for E. ovata. 
Bonnet ( 1930, cited by Levy 1970) found that Pirata piraticus prob- 
ably produces two generations per year. Another wolf spider, 
Lvcosa T-insignita, has a phenology similar to that of the filmy 
dome spider (Miyashita 1969). Two adult peaks occur, and as with 
N. radiata, adults that mature in the summer are smaller than 
spring-maturing individuals. Furthermore, apparently not all L. T- 
insignita complete two generations per year. 
Possibly modified bivoltine life cycles are characteristic of many 
small spiders in temperate regions. Casual, non-systematic observa- 
tions of the linyphiid Frontinella pvramitela (Walckenaer) suggest 
that this species may have two peaks in adult abundance each year 
(pers. obs.). The occurrence of two abundance peaks in a year, 
termed diplochronism by Tretzel (1961), occurs in several species of 
spiders (Toft 1976). However, Toft concluded that the phenomenon 
did not result from a mixture of biannual and annual life cycles for 
the species he studied in northern Europe, but instead occurred in 
species that had generation times of a year or longer. Conclusions 
about the ubiquity or rarity of both typical and modified bivoltine 
life cycles among temperate spiders must remain speculative until 
more evidence is gathered. 
