thumb|A pair of clicking stream frogs ([[Gray's stream frog|Strongylopus grayii) in amplexus]]thumb|[[Orange-thighed frogs (Litoria xanthomera) in amplexus]]
Amplexus (Latin "embrace") is a type of mating behavior exhibited by some externally fertilizing species (chiefly amphibians, amphipods, and horseshoe crabs) in which a male grasps a female with his front legs as part of the mating process, and at the same time or with some time delay, he fertilizes the eggs, as they are released from the female's body. Once a male has successfully attracted a mate, the process of amplexus begins, while the unsuccessful males are forced to continue their search for a mate through further calls. When a male amphibian attacks an amplexed pair of amphibians, he is trying to force the other male to release its grasp of the female, so he can then mate with her. After conducting experiments, researchers confirmed that amplexus does decrease a female's locomotor performance (e.g., swimming, walking) as well as the feeding rates. These two types of amplexus have been classified based on the position of the male amphibian relative to the female. This amplexus behaviour allows the amphibians' cloacae to be in close contact, while gametes are released. Additionally, amplexus is thought to help with the alignment of the reproductive tracts of both males and females, which furthermore contributes to successful fertilization. A female amphibian may not always be receptive to a male amphibian who is trying to initiate amplexus, as the female may not be ready to produce eggs. However, overall it was found that males have a higher level of corticosterone compared to females, as amplexus is seen as more energetically costly to males. However, multiple amplexus is not common among anurans, which could indicate that the costs associated with multiple amplexus are higher than the advantages associated with it.
Newts
In the case of newts, the process of amplexus is often observed soon after the newts become seasonally active. In the Western USA, for example, this time is typically soon after the onset of the winter rainy season, when intermittent streams and vernal pools become available as a breeding habitat. The rough-skinned newt is a specific widespread example of a newt in the western USA that can be observed in quiet stream pools and shallow ponds engaging in amplexus. During amplexus in newts, males will typically show the behaviour of tail fanning and chin rubbing which is thought to prompt the mating receptivity of the female newt. Studies have shown that male newts who have deeper tail-fins have better control of females during amplexus and are also more successful in catching the females for amplexus. A study examining the wrestling behaviour of newts found that of the observed wrestling encounters, 90% were "won" by the paired male, meaning he would retain the female newt. The first pair of walking legs is used to tightly clasp the female in all species, and the second pair is also employed in all but Limulus polyphemus. A male horseshoe crab develops modified claspers during sexual maturity when the male moults; these modified claspers can then help during the process of amplexus. The male's pair of posterior claspers are known for having the ability to maintain long-term amplexus which have been found to always attach to the female's opisthosoma during amplexus. If a male horseshoe crab has a damaged or missing clasper, then that puts the male at a disadvantage and increases the probability of being displaced by other competing male crabs. Crustaceans of the order Amphipoda engage in amplexus.