Provide heat to your colonies where they need it the most. Most species benefit from access to an area with heat; we see faster development. Usually, you could control the room temperature where the setup sits or often, it is easier to provide localized heat with a heating cable. 
 
Heating cables are beneficial in the ant keeping hobby due to their ability to heat multiple setups at once and how easy it is to direct heat to only a specific area, heat a small part of the nest and let the ants choose where to go.
 
We have two top-rated brands, "Zoo Med Repti Heat Cable" and "Exo Terra Heat Cable" both feature 15 watts of power, 3.5 meters long, are flexible and water-resistant. 
 
Both cables are very similar; although we have noticed the Exo Terra brand has a thicker silicone coating, the specifications indicate "Double silicone insulation".
 
We recommend using the heating cable through the top glass of formicariums that sit horizontally, through the front bottom if it sits vertical or the side, on test tubes, the cable can place it through the bottom of the front or the top middle section; we aim for the glass to eliminate potential condensation. The goal is always to have both cold and warm sections forming a temperature gradient.
 
Do not wrap cables around test tubes as they may get too hot; we also do not recommend placing a heating cable near a wet cotton ball, a water chamber or a water wall unless you are dealing with a high humidity species and you know what you are doing, heating a water source creates really high humidity levels that usually condensate on the colder areas, usually a recipe for disaster. 
 
Alternatively, we recommend using an electronically controlled thermostat to ensure the cable has an adjustable precise range and automatically turns on and off. Using a handheld thermometer, please ensure the heated area is not getting too hot (35C and up); we usually set our cables around 30 to 32C; if your house tends to get warm past 27C or 80F, it is advisable to monitor the cable temperature more closely. 
 
Exo Terra 15 watt cable shipping weight: 176 grams. 
Zoo Med 15 watt cable shipping weight:  127 grams.