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lokakuu 15, 2022

Micrathena

15 October 2022

The layer of ice on top of my birdbath this morning tells me that we finally had a good frost overnight. With temperatures dropping across the state, the number of spider observations added daily to iNaturalist has also precipitously declined. So go the seasons of Minnesota. I'm enjoying writing about some of our Minnesota spider genera and thought I would stick with the Araneidae for another post.

The orbweaver genus Micrathena is found throughout the temperate and tropical Americas with its highest species diversity occurring in the tropical forests much further south. Many of the members of this genus have horn-like spines and spikes on their abdomen that may help break up their outline and make them less visible to their predators. Some of them have white and black coloration which can make them resemble bird poop and may also help them to hide in plain sight. After all, who eats that? Their webs are typical of orbweavers with many radii, tight spirals and a central hub that is open (lacking spirals) (Dondale et al., 2003).

Minnesota is home to three members of this genus. These small orbweavers are most often found in wooded understories in the southern two-thirds of the state. Males are smaller and less conspicuously colored than the females.

M. mitrata or White Micrathena is our most common species in Minnesota. As its name implies, the female has a white abdomen with prominent spines on the posterior of its abdomen. It has been found from Pine County west to Stearns and Redwood Counties and southward within the Mississippi watershed. Ironically, the literature did not have any published records of this species in Minnesota when I first began my work on spiders back in 2009.

M. gracilis or Spined Micrathena has been most commonly reported from the southeast corner of the state (Wabasha to Houston Counties) but there is a record from Blue Earth County as well. Females of this species also have a white abdomen but it has prominent spines on both the sides and posterior of the abdomen.

M. sagittata or Arrow-shaped Micrathena is our rarest member of the genus. It has a more southern distribution and therefore is most likely to occur in the southeastern part of the state, particularly the Mississippi River Valley. This females of this species have a yellow abdomen and the spines at the posterior part of the abdomen are quite long.

White Micrathena: https://www.inaturalist.org/observations/92518296
Spined Micrathena: https://www.inaturalist.org/observations/138871756
Arrow-shaped Micrathena: https://www.inaturalist.org/observations/93322230

Sources
Dondale, C. D., Redner, J. H., Paquin, P. & Levi, H. W. (2003). The insects and arachnids of Canada. Part 23. The orb-weaving spiders of Canada and Alaska (Araneae: Uloboridae, Tetragnathidae, Araneidae, Theridiosomatidae). NRC Research Press, Ottawa, 371 pp.

Julkaistu lokakuu 15, 2022 07:05 IP. käyttäjältä cheins1 cheins1 | 2 kommenttia | Jätä kommentti