Arrow Shaped Micrathena
(Order: Araneae, Family: Araneidae)
Micrathena sagittata (photo by David Wickell) (Kansas, Sedgwick Co., Chisholm Creek Park 37.740704 N, -97.273746 W, near creek. 9/6/2012)
Description: This is one of the smaller species of orb-weaving spider. They are sexually dimorphic with the smaller male spider averaging 0.5 cm and females reaching up to 1.0 cm without including their legs. The most striking feature in both sexes consists of three large, pointed protrusions that come together to form the abdomen, giving them their distinctive arrow shape these are reduced or absent in males. Females have additional small spikes on the abdomen near the thorax. Both sexes have bright yellow abdomens rimmed to varying degrees in red. The thorax and legs are patterned with red and black.
Micrantha sagittata female (left) (photo by David Wickell) and male (right) (© Brett Tyler, 2008. From:http://bugguide.net/node/view/193810)
Adult Natural History: This species is diurnal and prefers to build its web near the ground in forested areas. The web consists of two portions, the frame and the orb. The frame is a relatively permanent structure and some individuals may leave it up for day or even weeks. The orb is built each day at dawn before being taken down in the evening and consumed by the spider. The spider leaves a hole in the center of its orb where it hangs upside down waiting for its prey. This gives it increased mobility and allows it to reach and immobilize its prey much faster. Little is known about nocturnal behavior or mating habits of this particular species.
Micrantha sagittata web. Note the open area in the center (© Stephen Bales, 2012)
Distribution: Micrantha sagittata is one of only three Micrathena species found in North America. It is most common in the eastern half of the country and only occurs in the eastern-most portion of Kansas. Nationally, it is found in nearly every state east of Kansas as far north as Maine.
Distribution map from Bug Guide (somewhat incomplete) (http://bugguide.net/node/view/2020/data)
Habitat: This spider is found in and around woodlands, building its web in the understory. It seems to prefer relatively moist micro-habitats.
Diet: Micrantha sagittata is polyphagous, eating a wide variety of insects. It has been shown that when given the choice, they will generally choose larger prey items.
Conservation Status: Least Concern (IUCN)
Díaz-Fleischer, F. Predatory behaviour and prey-capture decision-making by the web-weaving spider Micrathena sagittata. Canadian Journal of Zoology (2005) 83.2: 268-273
Milne, Lorus and Milne, Margery. The Audubon Society Field Guide to North American Insects and Spiders. New York: Knopf, (1980).
Submitted by: David Wickell, July 2013.