Theridion melanurum

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Current valid name

Theridion melanurum Hahn (family Theridiidae)

Recognition and diagnostic features

Small, dark brown with globose abdomen.

Related or similar species

Theridion dilutum, immatures of Latrodectus hesperus, Cryptachaea porteri.

Spider

Body lengths when mature: male: 2.8 - 4.6 mm, female: 3.0 - 4.8 mm

Immatures resemble miniature adults.

Egg sac

Description: spherical ball of bicolored tan-brown eggs very loosely covered with tannish silk, egg sac color caused by egg color, 3.06 ± 0.52 mm diameter

Number of eggs per sac: 57.91 ± 36.75

Size of egg: 0.55 ± 0.027 mm

Time of year eggs are likely to be laid: prior to harvest season

Distribution

In California: mostly along coastal regions throughout state

Elsewhere: eastern half of Washington and Oregon, British Columbia, Europe, North Africa, Siberia

This may be a naturally Holarctic species, and may be native to North America.

This species may not have been transported or become established outside of its range, but it is unclear whether it is a naturally Holarctic species.

Biology

Small cobweb weaving spider. Makes webs on grape leaves. Found in grape bunches. Female guards egg sac.

Status in table grapes

Level of Incidence: very common

Level of Concern in New Zealand: WPNZ (May 2010) nr, BORIC (Dec 2011) R, MAF-BPRA (2002) nr (coding definition)

Level of Concern in Australia: WPAU (2006) nr (coding definition)

Level of Medical importance: none

Common name

None for species, combfoot spiders for family

Taxonomic history

Stable

Selected references

Levi, H. W. 1957. The spider genera Enoplognatha, Theridion, and Paidisca in America north of Mexico. Bull. Amer. Mus. Nat. Hist. 112: 1-124.