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Edible frog |  |
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Marsh frog | |
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Pool frog | |
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Midwife toad | |
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Bullfrog | |
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| *Note that a particular form of the pool frog is now believed to be native to England and is subject to a reintroduction programme. | ||||
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When calling, bullfrogs inflate a single vocal sac under the throat rather than the two sacs on either side of the head like the marsh frog (see above). | ||
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Bullfrogs do not have dorsolateral ridges which are usually prominent in marsh frogs (see above). | ||
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The calls of the two species are different; bullfrog calls are reminiscent of cattle while marsh frog calls are more likely to be mistaken for waterfowl. |
These are small toads that rarely exceed 5cm in length. They have an unusual mode of reproduction; males carry strings of eggs wrapped around the hind legs. These toads can be difficult to find as by day they hide away in dark, damp crevices under large stones or pieces of timber etc. The easiest way to detect and identify this alien is by its distinctive call which sounds like an electronic 'bleep'. Midwife toads call in late spring, especially during May, but also sporadically on warm nights later in the year. |
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Midwife toads seem quite able to survive in the UK and a population has been living in Bedford for over 100 years. They do not seem to travel far - at least under their own steam. Most known populations are still confined to the Bedford area, but occasionally midwife toads pop up elsewhere presumably as a result of being moved by people. |
Many terrapins originating from the pet trade are capable of surviving the UK climate, but they do not seem to be able to breed successfully. Hence, many terrapin sightings are of released individuals. Occasionally, especially in publicly accessible ponds in residential areas, they are found in some numbers, which seems to be a result of many pets being dumped in the same pond - possibly for 'company'. There is no current estimate of numbers in the wild, but it seems likely that thousands have been released across the UK. Many released terrapins are red-eared terrapins (shown above) from North America. The import of this species into the EC is now illegal but the animals are long-lived and can still be found in the UK, as can other terrapin species. The calls on this website have been kindly provided by Helen Muir-Howie, Julia Wycherley and The HCT. |
Identifying aquatic aliens |
Alien Encounters welcomes your sightings of any non-native amphibian and reptile. Below are four types associated with aquatic environments such as ponds and lakes. When these species are present at a site they are fairly easy to detect. In the case of the frogs and midwife toad, their calls give them away. Our native common frog and common toad breed early in the spring and do not have very loud calls. The alien species, on the other hand, breed in late spring or early summer and call loudly at this time as well as sporadically through the warmer months of the year. |
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Green/water frogs | ||
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North American bullfrog | ||
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Midwife toad | ||
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Terrapins |
These include several species (edible frog, Iberian water frog, marsh frog, pool frog* etc.), some of which interbreed. It is difficult to distinguish the different species and coloration within a species, especially the marsh frog, is variable (see below). The background colour can be green, brown or grey. Green coloration can be vivid. Some have a light stripe running along the back. |
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When calling, they inflate vocal sacs on either side of the head as shown in the photograph to the right. Note also the dorsolateral ridge running from behind the eye towards the hind end of the frog - useful in distinguishing large water frogs from the North American bullfrog (below). They are much more aquatic than our native common frog, remaining in and around the water all year (most common frogs spend a good proportion of the year on land). They like to sunbathe and can be seen basking by the side of ponds. |
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This is a huge frog which can grow to 15 cm long. But in spite of its size, the bullfrog is wary and can be difficult to get a good look at. It does, however, vocalise very loudly on warm nights during the summer making it easily identifiable as its calls are reminiscent of the mooing of a cow. Due to the ecological threats posed by this species, its import into the EU has been banned and, as such, the chances of finding bullfrogs in the UK are now slim. Nevertheless, a single population did go unnoticed for some years in southern England so it is important to maintain vigilance with regard to this frog. 
In spite of the variability in coloration, there are several characteristics that all green/water frogs share. They are noisy, calling during late spring and sporadically through the summer.