Earthworms are considered to be the primary component of the soil ecosystem and its temperature. Olfactory cues play a central role in the various earthworms' attractions to particular chemical cues and food sources. Olfaction is the sensory modality that the earthworm uses to obtain various information in its surroundings. Olfaction helps different organisms also in perceiving semiochemicals, which include both kairomones and pheromones (Zirbes et al., 2011). The identification of chemoreceptors on the earthworm's buccal epithelium and prostomium help in the detection of quinine, glucose, and sucrose. It is indeed true that olfaction as used by the earthworms, aid in their collective movement coordination.
The adaptation of the earthworm towards olfactory cues helps in response to its environment. The chemical cues towards food helps in technique development in sampling and extraction of earthworms if any study is to be done, such as, vermicomposting (Domínguez, Aira & Gómez-Brandón, 2010). Also, there are behavioral techniques employed for such chemical cues' approaches including chemical extraction, mechanical vibration, electrical extraction, and heat extraction. For instance, the use of chemical extraction methods through the use of either irritants or natural repellents such as exotic-plant extracts, mustard extract, and formalin have certain advantages over other existing chemical methods. Earthworms are dependent on attraction as opposed to repulsion.
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The earthworm's sensory modality and reaction towards stimulus are similar to the human's responses in terms of reflex. During crawling, there is a muscle contraction in a given segment that stimulates the earthworm's stretch receptors. Impulses are then carried to the cord over the sensory nerves leading to the motor neurons sending to the longitudinal muscles the said impulses (Reddy & Rao, 2008). As a result, the stretch muscles are activated through the pull made by the longitudinal muscles that make contraction moves happen. The similarity in humans about the withdrawal reflex is that when there is a stimulus detection, neurons help in receiving the nerve signal until they reach to the brain's central nervous system (CNS). Impulses that generate from the motor nerves help in contraction due to the stimulus.
Conclusion
Earthworms use olfactory cues in response and perception of their surroundings. Olfaction as used by earthworms, aid in comprehension of how they coordinate their behavior and orient themselves. Earthworms have a sensory modality that is also homologous to humans such as the contraction/withdrawal stimulus.
References
Domínguez, J., Aira, M., & Gómez-Brandón, M. (2010). Vermicomposting: earthworms enhance the work of microbes. In Microbes at work (pp. 93-114). Springer, Berlin, Heidelberg.
Reddy, N. C., & Rao, J. V. (2008). Biological response of earthworm, Eisenia foetida (Savigny) to an organophosphorous pesticide, profenofos. Ecotoxicology and Environmental Safety, 71(2), 574-582.
Zirbes, L., Mescher, M., Vrancken, V., Wathelet, J. P., Verheggen, F. J., Thonart, P., & Haubruge, E. (2011). Earthworms use odor cues to locate and feed on microorganisms in soil. PLoS One, 6(7).
