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Daddy long-legs

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by Tim Blackburn
Publish date
20 September 2011
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Recently, a visitor to Bugs Alive! asked me whether daddy long-legs are spiders. The answer depends on what one is referring to when employing the term "daddy long-legs". It can be used to refer to a group of close relatives of spiders known as the harvestmen, which are arachnids (as are spiders) but are nonetheless not spiders. It can also be used to refer to crane flies, which are insects and not arachnids. The term is, however, most commonly used in Australia to refer to a species of spider known scientifically as Pholcus phalangioides. P. phalangioides is also sometimes known as the grandaddy long-legs, the cellar spider or the house spider, and is commonly found in houses in its irregularly structured webs which it often weaves in dark areas, such as under desks and behind bookshelves, or in the corners of ceilings in disused rooms.

The spider Pholcus phalangioides The spider Pholcus phalangioides is commonly referred to as the "daddy long-legs".
Image: Tim Blackburn
Source: Museum Victoria

Harvestmen, however, live in vastly different environments than does Pholcus phalangioides. They have been found in moist leaf litter, under rotting logs, under rocks and under the bark of trees. Unlike spiders, which are classified under order Araneae, harvestmen are classified under order Opiliones. The cephalothorax (the anterior/front body segment) of harvestmen is fused broadly with the abdomen (the posterior/rear body segment) to form a body which seemingly lacks a waist, whereas there is a distinct division between these two body segments in spiders. Furthermore, harvestmen have two eyes which are each positioned on the end of stalk-like projections found in a region approaching the top of the cephalothorax, as compared with spiders, which generally possess eight eyes attached directly to the anterior (front) region of the cephalothorax.

Harvestman specimen
Harvestmen are commonly referred to as “daddy long-legs” but they are not spiders. The above specimen’s second right leg appears blurry because harvestmen use their second pair of legs much like antennae, constantly waving them around.
Image: Tim Blackburn
Source: Museum Victoria
 

Harvestman on a leaf The two body segments of harvestmen are fused to give the appearance of a body with a much reduced or absent waist.
Image: Patrick Honan
Source: Museum Victoria
 

Unlike spiders, harvestmen do not produce silk, and they are omnivorous, having been known to feed on other invertebrates, plant matter, and the rotting carcasses of birds and mammals. They are non-venomous but can chew their food, whereas spiders must use venom injected by their fangs to convert their prey to liquid which they drink. Male harvestmen have a penis, which facilitates the direct transfer of sperm (from the genital region) to the female, whereas male spiders must use their pedipalps (which encircle the mouth) to do this indirectly.

Pholcus phalangioides
The distinct division between the two body segments of Pholcus phalangioides gives the appearance of a waist.
Image: Tim Blackburn
Source: Museum Victoria
 

Pedipalps of Pholcus phalangioides The bulbous terminations to the male’s pedipalps of Pholcus phalangioides are used to transfer his sperm to the female.
Image: Tim Blackburn
Source: Museum Victoria
 

pedipalps of harvestmen The pedipalps of harvestmen are used for food-handling only as males have a penis which enables the direct transfer of sperm to females.
Image: Tim Blackburn
Source: Museum Victoria
 

The Live Exhibits department sometimes has harvestmen in its collection. We are considering the merits of putting them on display in the near future, possibly to illustrate the differences between spiders and harvestmen.

Harvestman. A harvestman I recently found inside a house, oddly enough.
Image: Tim Blackburn
Source: Museum Victoria
 

Further reading:

Harvey, M. S. And Yen, A. L. (1997) Worms to Wasps. Oxford University Press, Oxford: p. 86-87.

Milledge, G. A. and Walker, K. L. (1992) Spiders Commonly Found in Melbourne and Surrounding Regions. Royal Society of Victoria, Melbourne.

Links:

Question of the Week: Daddy long-legs spiders

Harvestmen (CSIRO)

Harvestmen (Wikipedia)

Pholcus phalangiodes (Wikipedia)

Pholcidae (Wikipedia)

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