It can be difficult to identify the culprit just from 'bite' marks. Bed bugs, fleas, mosquitoes, sand flies, spiders and other can bite. Sometimes allergic reactions to other things in our environment are mistaken for insect bites.
In general it can be very difficult to identify the culprit just from the 'bite' marks. There are however some indications that can help to identify what pests, if any, might be responsible.
Spiders > bites involving venom usually cause pain prior to inflammation. If there appear to be two puncture wounds at a bite site this may indicate a spider is the culprit; spiders use two fangs to bite and inject their venom. (How to control spiders)
Mosquitoes > Mosquitoes are well known for their biting habits. Mosquitoes are blood sucking flying insects and in tropical areas they frequently carry and transmit serious diseases including malaria, dengue fever, and others. In New Zealand mozzies rarely carry disease but there is concern that if the world warms up due to global warming, northern parts of New Zealand would be vulnerable to disease carrying mosquitoes. Mosquitoes, as with other blood sucking pests, inject anaesthetic and anti-cogulant when they suck blood. It is the proteins in these that cause allergic reactions in some people. Causing reddened raised itchy lumps at the bite site. It can be difficult to tell if the bite was caused by mosquitoes another biting insect. (How to control mosquitoes)
In general mosquitoes bite at dusk or and attack exposed skin areas where blood is close to the surface; neck, arms, ankles, and legs.
Marks > With insect or spider bites a puncture wound is usually visible and often includes the release of a small amount of blood.
If no puncture wound is found it is possible that a red mark and swelling is due to some other skin reaction or damage to the skin caused by some other physical injury.
Bites tend to form similar sorts of localised reddening and swelling because the marks are caused by our immune systems reacting to foreign substances; whether proteins in the anti-coagulants and anaesthetics that blood sucking insect inject or just the physical damage caused by the bite.
Just talking about fleas or bed bugs commonly makes people feel itchy and scratch the skin in response. Scratching can cause reddening and inflammation that can be mistaken for bites. It is therefore not easy for medics or pest experts to identify red marks as bites never mind being able to identify the possible culprit.
Dust, chemicals (natural or synthetic) and others can cause allergic reactions that include raised red itchy marks and these can be mistaken for insect bites. The waste products of the house dust mite is frequently the cause of allergic reactions of the skin as well as asthma.