Leucochloridium paradoxum

The range of Leucochloridium paradoxum follows that of its host, snails of the genus Succinea that live in Europe and North America. (Dawes, 1946; Rennie, 1992)

The worm is both an endoparasite of Succinea snails and of various birds such as crows, jays, sparrows and finches. It encounters these animals in temperate forests of North America and Europe. The egg is the only stage of development that exists outside of a host but it must remain moist to survive. (Dawes, 1946; Rennie, 1992)

The worm has different microscopic sizes and shapes throughout its development. Their eggs are brown and oval shaped. After hatching, the miracidia, or first stage larvae are clear and elongate. After transformation, the miracidia become sack-like objects called sporocysts. The sporocysts cause the eyestalks of their snail hosts to pulsate yellow, green, and red. Some sporocysts then give rise to cercaria, or juveniles, which then have tails and a more complex digestive tract. The cercaria have a lined excretory bladder which extends into their tails a bit and the tails also have finfolds on the top and bottom as well as setae on the sides. The cercaria aslo have wo eyespots. These cercaria quickly become an encysted metacercaria from which emerge the adults. The adults are spined, long, dorsally flattened, and have suckers for attachment within their definitive hosts. (Fried and Graczyk, 1997; Roberts and Janovy Jr., 2000)

After a succinid snail ingests the worm's eggs, the sporocysts that arise from the miracidia have one of two destinies. Some sporocysts give rise to cercaria and others asexually produce more daughter sporocysts. When a bird ingests the snail, the remaining sporocysts become cercaria, which eventually develop into adults. The adults are monoecious, or hermaphroditic, although they can cross fertilize when in close proximity. The resulting eggs are released by the worms in the rectum and excreted by the bird host along with its feces. (Erasmus, 1972; Fried and Graczyk, 1997; Roberts and Janovy Jr., 2000)

For Leucochloridium paradoxum to continue development, it must be consumed by a snail of the genus Succinea. Once inside a snail, the eggs hatch into miracidia that then become sporocysts. Sporocysts accumulate in the hepatopancreas of the snail and in a broodsac in the head-foot of the host. Many sporocysts move to the tentacles of the snail. (Brand, 1979; Dawes, 1946; Rennie, 1992; Roberts and Janovy Jr., 2000)

Bristles and small spines probably act as tactile receptors, and these animals may have reduced chemoreceptors. (Brusca and Brusca, 2003; Roberts and Janovy Jr., 2000)

Leucochloridium paradoxum is an endoparasite of the rectum of birds as an adult. There it feeds on passing digested matter. It shows little definitive host specificity as it is known to parasitize more than fifteen bird species including crows, jays, sparrows and finches. As a sporocyst, the worm absorbs nutrients through its tegument from its intermediate hosts, Succinea snails. (Dawes, 1946; Roberts and Janovy Jr., 2000)

These animals are probably not preyed on directly but are ingested. Egg and larval mortality are high since the parasites often do not reach appropriate hosts.

The worm is both an endoparasite of Succinea snails and of various birds such as crows, jays, sparrows and finches. It encounters these animals in temperate forests of North America and Europe. The egg is the only stage of development that exists outside of a host but it must remain moist to survive.

The parasitism of Leucochloridium paradoxum on succinid snails has no effect on humans. In their definitive bird hosts, they inhabit the rectum where they essentially feed on waste that is about to be excreted so their pathogenic effects on their hosts and ultimately on humans are negligible.

Leucochloridium paradoxum presents no known benefits to humans.

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Two visible changes in the snail occur as a result of the accumulation of sporocysts. First, the snail's tentacles enlarge and pulse in vivid colors. Secondly, the instinctively photophobic snail becomes photophylic and climbs to the tops of trees and grasses. This conspicuous sight looks like a caterpillar to passing birds. The birds swoop down and consume the snail and unknowingly inoculate themselves with Leucochloridium paradoxum. The worm continues its development within the bird's gut and ultimately ends up in the rectum where its eggs are flushed out with waste. Another snail consumes the excreted egg and the cycle continues. How the worm is able to cause such a drastic change in Succinea is still unknown. (Brand, 1979; Dawes, 1946; Rennie, 1992; Roberts and Janovy Jr., 2000)