Coleosoma blandum

Coleosoma blandum is a species of cobweb spider in the family Theridiidae. It has a widespread distribution across Asia, from India and Sri Lanka through Southeast Asia to East Asia, including China and Japan. The species has also been introduced to the Seychelles and Hawaii.^[1]

The species was first described by O. Pickard-Cambridge in 1882 from a male specimen collected in Sri Lanka (then Ceylon).^[2] The species was initially placed in the genus Theridion by some authors, but was transferred to Coleosoma by Levi in 1959.^[3]

Two species described by Thorell in 1895 from Myanmar, Theridion acrobeles and T. conutum, are now considered junior synonyms of C. blandum.^[2]

C. blandum is widely distributed across Asia, with records from India, Sri Lanka, Bangladesh, Myanmar, Thailand, Philippines, China, and Japan.^[1] In Japan, it occurs on Honshu, Kyushu, and the Ryukyu Islands (including Amami Ōshima, Okinawa Island, Iriomote Island, Ishigaki Island, and Yonaguni).^[2] The species has been introduced to the Seychelles and Hawaii.^[1] There are also multiple finds from Réunion.^[4]

C. blandum is commonly found in agricultural areas and is considered a beneficial predator in rice fields throughout Southeast Asia.^[5]

C. blandum is a small spider with females measuring 2.0-2.8 mm and males 1.9-2.6 mm in body length. The carapace and abdomen are black, while the legs are yellowish-white with black rings on the tips of the tarsal segments and base of the metatarsal segments of the fourth legs.^[2]

The male is distinguished by its greatly enlarged and swollen abdomen with a distinctive sac-like posterior portion. The female can be identified by multiple thread-like protrusions that emerge from the abdomen. Both sexes have a large yellowish-white spot in the center of the dorsal surface of the abdomen.^[2]