There are two kinds of spiders that we call daddy long legs (DLL). One is the "true" DLL and it is not a true spider, but instead is a related arachnid called a Harvestman. This one is not venomous and does not make webs, but only wanders around feeding on live or dead insects. It has a fatter body than the other kind, which is the daddy long legs "spider", more properly referred to as a Cellar Spider. This one is the messier kind, with dense webs that gather a lot of dust and left over pieces of bugs, and probably is the one most responsible for the "cob webs" inside homes and under the eaves outside. I suspect this is the DLL you are referring to as it is the more common kind indoors. And, by the way, the MYTH that the DLL has the most toxic venom of all spiders is just that, a myth. Apparently the DLL spider's venom is no more or less toxic than any other typical spider and it is not even capable of biting people. It's fangs are just too small.
It is amazing how rapidly the DLL occupies areas around a home, but they do so for one reason - they find food. These spiders feed on tiny flying insects like gnats and mosquitoes and other bugs that are active around a home, particularly around exterior lighting. So, here is one way to reduce the numbers of spiders around the outside of the home. Turn off the lights at night where they are not needed, and consider changing the bulbs to yellow bulbs for lights that are needed for safety or security. Yellow is much less attractive than white and FAR less attractive than mercury vapor lights, just in case those are in place. If so, those could be changed to sodium halide, a more orange color but just as bright as mercury vapor. Managing lighting means less spiders on the outside which means less spiders finding the opportunity to get inside.
But, some will still make it, and I am a strong advocate of using a vacuum cleaner to remove the spiders and their webs on the inside of my own home. I only need to do this occasionally, and the careful use of the vacuum completely removes the unsightly, dirty web without smearing it all over the wall. I think it is appropriate always to look the non-toxic but still effective ways to control arthropod pests on the inside, and a vacuum is just as much a tool for professional pest technicians as are the chemicals. Even on the outside a vacuum may be the perfect tool for removing both spiders and webs, particularly on 1-story structures. Most companies now also use the "Webster" style brushes to remove the webs following each service, as this removes the visible evidence of a pest that would otherwise continue to annoy a homeowner.
All spiders are extremely susceptible to Synthetic Pyrethroids, so these can be used both to kill and perhaps to repel the spiders from treated surfaces. They can be used around the exterior of the foundation, around windows and doors, and along other "pathways" where the spiders are likely to travel to get inside. Be very careful now in the U.S. to adhere to the new restrictions on the use of pyrethroids on exterior surfaces, but under the eaves they still can be used as a general application. Most of them also can be used indoors, but it just seems so much faster to remove the spiders and webs with a vacuum. And, spraying a web with a liquid spray is likely to paste that webbing onto the surface where it is far more difficult to remove later. We now have the new Suspend Polyzone that, according to the manufacturer, will provide up to 90 days of effective residual even on outside surfaces.
Finally, take a strong look at exclusion, both for your own home and for customers. Spiders need openings to get inside, other than coming in through open doors and windows or being carried inside on materials brought in from outside. The use of weather stripping, caulking, and other exclusion materials is a permanent way to keep all kinds of bugs from moving into the home.
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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.