Biotic Inventory:
Documenting Diversity at the Katharine Ordway Natural History Study Area
Lumbricus terrestris, the Common Earthworm
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Taxonomy
Kingdom Animalia
Phylum Annelida
Class Clitellata
Order Oligochaeta
Family Lumbricidae
Genus Lumbricus
Species terrestris
Examples of common names: Earthworm, Nightcrawler, Field worm, Manure worm
Diagnostic Characteristics
Worms are one of the most identifiable animals
worldwide, but there are few diagnostic characteristics to consider.
The most notable external feature is the segmentation of the body,
which is clearly visible in Figures 1-4. The first section of the worm,
the anterior section or head, consists of the mouth and the prostomium.
The prostomium is a lobe that serves as a covering for the mouth and as
a wedge to force open cracks in the soil into which the earthworm may
crawl 1. The anterior section of the worm is shown in Figure 1.
Another key characteristic is the clitellum, or the collar-like
structure near the front of worm’s body. The clitellum is used to
distinguished adult worms from juvenile worms because it is a feature
present only in adult worms 2. The collected specimen was lacking a
clitellum and, therefore, must be a juvenile.
Another noticeable external feature of worms are the small hair-like
structures, called setae or bristles, which are located on each
segment. These can be extended or retracted and act as the principal
function for movement 1. Setae are visible in Figures 1 and 3. Other
essential features of worm anatomy are the various skin glands that
secrete lubricating mucus, which aids movement through the earth and
helps to stabilize burrows and casts 1. This is not visible in any of
the Figures because the specimen was preserved in ethanol before
photographing, but when it was collected it was actively secreting
mucus and covered in the lubricating substance. Worms can range from a
few millimeters long nearly a meter, but most common species are a
10-20 cm long 1.
The specific specimen identified is 4.8 centimeters (Figure5.). The
body segmentation was visible when the specimen was collected and mucus
was being actively secreted. After being preserved in ethanol, the
setae were easily identifiable on each segment and the anterior and
posterior sections were easily distinguished from one another. The worm
changed color after being preserved in ethanol; when collected it was a
brownish-pink and after being preserved in ethanol it had paled to a
beige color.
Ecology
Worms are found in the soil and leaf litter of every
continent except Antarctica. The majority of temperate and many
tropical soils support significant worm populations, while grasslands
and temperate woodlands can support much larger populations of worms 3.
In general, deciduous woodlands and orchard soils support the highest
numbers, and temperate soils tend to support higher number than
tropical soils. The amount of individual worms in any given square
meter of soil (any soil type) from any given continent can range
anywhere from zero to 800 worms 4.
Worm behavior varies according to temporal changes,
climactic changes and species-specific behavior. Different species of
worms prefer different habitats and live in different ways. Young and
immature worms are usually found nearer the soil surface, with most
adult worms being found in around 15cm of soil. Temperate worms live
deeper in the soil during the winter when the surface of the soil is
colder. In times of water shortage, some species will burrow deeper
down into the soil seeking moisture while others, which are better at
tolerating desiccation, remain nearer to the surface 4.
Worms are beneficial to their surroundings in some
ways and interact with other members of the food web in their
ecosystem. Worm castings are rich in all the minerals necessary for
plant growth in a water soluble form that are immediately available for
plant use. Worms improve the structure of the soil by bringing
nutrients up to the surface layers of the soil from deeper down and
they assist in the break down of organic matter in or on the surface of
the soil 4.
Worms continuously interact with the environment and
organisms around them. Worms derive their nutrition from fungi,
bacteria and possibly protozoa and nematodes, and they promote the
activity of these organisms by shredding and increasing the surface
area of organic matter and making it more available to small organisms
3. Worms, thus, act as providers for smaller organisms. Worms influence
other organisms that inhabit the soil because they alter the amount and
distribution of organic matter and microbial populations 3.
Life History
Worms are hermaphroditic, meaning each worm contains
both male and female sex organs. The male and female sex organs can
produce sperm and egg respectively in each worm. Although worms are
hermaphrodites, most need a mate to reproduce. During mating, two worms
line up inverted from each other so sperm can be exchanged. Each worm
has two sperm openings and two sperm receptacles, which take in sperm
from another mate. The worms have a pair of ovaries that produce eggs.
The clitellum will form a slime tube around it, which will fill with an
albuminous fluid. The worm will move forward out of the slime tube. As
the earthworm passes through the slime tube, the tube will pass over
the female pore picking up eggs. The tube will continue to move down
the worm and pass over the male pore called the spermatheca which has
the stored sperm called the spermatozoa. The eggs will fertilize and
the slime tube will close off as the worm moves completely out of the
tube. The slime tube will form an “egg cocoon” and be put into the soil
5. The eggs will hatch after about 3 weeks. Each cocoon produces a
range of two to twenty baby worms with an overall average of four baby
worms per cocoon 1.
Distribution
Worms are found on every continent in the world
except Antarctica. They are indigenous to Europe, but are now abundant
in North America and western Asia 6. This is most likely due to
settlers bringing the worms to newly settled territories, which is how
most non-native species first inhabit a completely new area.
Voucher Information
This specimen was collected in a woodland area
(Figure 6.) from the underside of an over-turned log at the Katherine
Ordway Natural History Study Area in Inver Grove Heights, Minnesota.
The specimen was in dark, moist soil amongst decaying leaves where the
decayed log had been before being dislodged (Fig. 7. &8.).
Figure 6.
Figure 7.
Figure 8.
References
1. University of Florida Department of Entomology. 2009. http://edis.ifas.ufl.edu/in047
2. Great Lakes Worm Watch. 2006. http://www.nrri.umn.edu/worms/identification/guides.html
3. United States Department of Agriculture. 2010. http://soils.usda.gov/sqi/concepts/soil_biology/earthworms.html
4. Earth Life. 2010. http://www.earthlife.net/inverts/oligochaeta.html
5. University of Pennsylvania. 2010. http://www.sas.upenn.edu/~rlenet/Earthworms.html
6. National Geographic. 2010. http://animals.nationalgeographic.com/animals/invertebrates/earthworm/
7. Global Biodiversity Information Facility. 2010. http://data.gbif.org/species/browse/taxon/14850241
Compiled by Meghan Davies.
Biodiversity & Evolution (BIOL 270) Professr Sarah Boyer. Spring 2010
Specimen collected at Macalester College’s Katharine Ordway Natural History Study Area on April 15, 2010