Definitions

Labium the lower lip of an insect
Labrum the upper lip of an insect, also the outer lip of a gastropod shell
Lacewing an insect in the Neuroptera Order
Ladybird/ladybug a beetle in the Coccinellidae family
Lamarkism Inheritance of acquired characters. The theory that changes in use or disuse of an organ result in changes in size and functional capacity of the organ, and that these modified characters are transmitted to the offspring.
Lampyridae glow worms or fire flies.
 
Lampshell Brachiopoda
Lancelets a group of animals in the phylum Chordata. Often used to study the primitive features of animals with notochords.
Land bridge a land connection between 2 or more adjacent landmasses which can be a route for migration or dispersal of terrestrial organisms.
Larva An immature stage which is radically different in form to the adult, e.g. caterpillar.
LD50 the dose required to kill 50% of the organisms in a test population per unit of time
Leaf beetle Chrysomelidae
Leaf miner a feeder on the mesophyll layer between the upper and lower epidermis of a leaf
Leatherjacket Tipulidae
Leech Hirudinea
Lek an area where animals assemble for communal courtship display and mating, e.g. male midges dancing in the air in a tight group while the females sit below and watch
 
Lepidoptera butterflies and moths
Life cycle The sequence of events from the birth of an individual to its death. The stages through which an organism passes between the production of gametes by one generation to the production of gametes by the nest, e.g. the bumblebee life cycle.
Life history The significant features of the life cycle through which an organism passes, with particular reference to strategies influencing survival and reproduction.
Life span Longevity. The maximum or mean duration of the life of an individual or group.
Life tables tables of data summarising mortality in populations
 
Limiting factor Any environmental factor, or group of related factors, which exist at sub-optimal level and so prevent an organism from reaching its full biotic potential.
Limnology The study of lakes, ponds and other standing waters and their associated organisms.
Limpet A mollusc
Lineage a line of common descent
Linguatulida a.k.a Pentastomida or tongue worms
Linnean classification the system of hierarchical classification and binominal nomenclature established by Linneus
Lithosphere the rocky component of the earth's surface
Litter Recently fallen plant material which may be partly decomposed
Littoral living between the low tide and high tide marks
Local stability the tendency of a pop to return to its equilibrium after a small perturbation
 
Longevity The average lifespan of individuals of a population under a given set of conditions.
long-horned beetle Cerambycidae
longitudinal running from front to back
looper aka inch worm, the caterpillar of Geometrid moths, so-called because of the looping locomotion
Lophophore the circlet of eversible ciliated tentacles surrounding the mouth of certain sedentary aquatic animals
Lorica the protective, external case found in some rotifers, etc.
Loricifera a phylum of microscopic invertebrates
Lucanidae Stag beetles
Luciferous Light producing, luminescent, e.g. the European piddock, glow-worms
Lug worm A polychaete worm
Luminescence chemical production of light, e,g, as in the European piddock, glow-worms
Lungs the evaginated respiratory surfaces of terrestrial animals that connect to the atmosphere by narrow tubes, e.g. book lungs in spiders
Lycaenidae The butterfly family which contains the Blues, Coppers, and Hairstreaks
Lycosidae Wolf spiders and hunting spiders